How old is he?

A lot of men, of a certain age, start to have problems preforming.

If he's on medication (for depression, high blood pressure, or pretty much anything) it might also be affecting him.

First stop...his doctor's to get a check up.

He just turned 25. For some reason he refuses to make an appointment. We've had the same fight for a few years and nothing has changed. I think that maybe it's just time to move on.

Ok, initially I can see it being medication or a medical problem, until you mentioned he comments on your stomach. I have a very low tolerance for negative comments about any part of my body. If my husband ever did that, it would be a huge problem for me. Evaluate the relationship. If he's kind and loving and you feel close to him outside of sex, then maybe it's something you guys can work on. But if in general you feel like he's distancing himself from you, if you think he's no longer attracted to you, it may be that you need to move on.

He talks about your stomach? There's your problem. I had a very verbally abusive husband, and he was constantly making comments about my stomach and my weight after I'd given birth to our son. He was very toxic and I am so glad I got out of that relationship. Sounds like 25 year old non-lover boy may need a big boot in the butt! If he isn't feeling it, go feel it with someone that appreciates you! I promise, it isn't you. I can tell you are super confident and that is very attractive to most men. Use that confidence and find someone that can help you boost it even more - you deserve that much.

The comments about your stomach concern me as well. I've spent 20 years working to convince my wife she's beautiful and would never say anything derogatory about her body or weight. EVER. I wonder if he is dealing with depression, or if he's addicted to pornography -- or both. At the very least physical touch may not be his love language, and if it's yours then you're probably really, REALLY struggling in all of this. It kind of sounds like you already have one foot out the door. My personal mantra when it comes to relationships in crisis is "fix it or end it." Life's too short to settle for mediocrity. Some relationship challenges take years to overcome, and that can be okay as long as there's a plan and communication and it's going somewhere (and if the relationship is worth saving). I don't know how the other aspects of your relationship with him are, but even if they're great the sexual dysfunction could still be a deal breaker. I would write down what you are looking for in a relationship, then compare it to what you actually have. It could be an eye-opening exercise. (And seriously, what kind of guy closes his eyes during sex? My wife makes me turn off the light because she is self-conscious, but I'd leave them on if it were up to me!) I can relate to the kissing thing but ONLY when I am self-conscious about my breath (like when I had curry for dinner).

HI and Welcome Baffled... I think you've been given some really good advise here... Big hug....xo

What does he say about your stomach?

What does HIS stomach look like? How ambitious is HE in other areas of his life, like work and exercise?

How does he treat you at other times, in other situations? Is he kind and loving to you, or do you feel it's become more of a friendship or even "roommate" situation?
Commenting about your body is NOT cool. It's unkind, and it honestly sounds like he is trying to upset you to avoid the intimate situation altogether.
I hate to jump to this, but it makes me wonder if he's not "getting it" elsewhere, either with another person, or online, or pornography, etc. It's not very common for a 23-25 year old male to just "not be into sex" at all, in some form. It may very well be that he is cheating, is gay, has a porn addiction, has a fetish, something he feels the need to hide from you.
Regardless of what is causing it though, you deserve more. If he is unwilling to talk through it, get help somehow, address it, etc, then I would be questioning if it is worth staying? Unwillingness to work through a problem in a relationship, regardless of the nature of the problem, is not a good sign.

Unless he's commenting on how beautiful your stomach is, there really is nothing cool about commenting on your stomach, period. Or really any part of your body, unless you ask for his opinion.

It shows a real lack of empathy for a man to criticize his partner's body, ANYTIME, but especially when they are having sex! A woman is at her most vulnerable then, and unless he's a real dim wit, he knows that. Which leaves the possibility he is deliberately trying to hurt her. I'd confront him about this, have a discussion, and then if he continues to do it (or any other abuse), get out fast.

Ugh... I am so sorry.
It is hard for me to say this, but I think he has lost his attraction to you.
I think it is time to take a break from your relationship and just tell him you need a break. If he asks you why, I wouldn't tell him the reason just yet. You can tell him that you are unhappy and it would be the truth.
After that, watch what he does .
If he truly loves you, he will make all tempts to keep you and this would rekindle your sex life but if he doesn't - you will know that he is basically done.
It is a terrible thing to go through , but you are not his wife... You should not have to live in this anxiety and suffering.
Let him think about it and in the mean while, work to get your self esteem back after he just crushed it with his behaviour.
I ve had a number of sexless relationships and it just doesn't work. Especially at this age.
You deserve better .

Thank you all for the support! I really needed it. Here are some answers to your questions:
OTM64: About my stomach (embarrassing), he asks if I need to poop. I'm very thin so after I eat I bloat. He doesn't say anything like, "Your stomach is getting bigger" or "You need to lose weight." I discussed it with him about how it makes me feel super self-conscious and I told him that if he doesn't go to the doctor to figure out what is wrong with him, I will leave because it's not fair for me to stay.
koolman: He has an amazing body. He has really toned abs and body. He's thin as well but doesn't bloat as badly as I do when we eat. He's very ambitious about life and work. He is self-employed and working on a triple engineering degree. He's extremely intelligent and attractive. It gets really intimidating at times.
happymama2j: When we are intimate, he sometimes rubs my stomach and says how beautiful I am. He's kind and loving in any other situations in life. He's supportive and is always there when I need to talk about something that is bothering me. It's just intimacy that has been the issue for the past few years. I definitely do not want to leave because I love him more than anything and we work really well together as a couple. He's always stressed about something and he never seems to think about having sex as a way to relieve that stress. Maybe this whole problem is my own insecurities about not being as intelligent nor as attractive as he is. His past girlfriends and his friends who are girls are model-level attractive whereas I feel like I'm very average. Cute, but average.

I concur with Happymama2j, at his age, it makes no sense that he doesn't have a desire to have sex. I'd also think he's probably getting it somewhere else, cheating on you, flirting beyond what's acceptable when you're in a relationship, is dallying in something he knows would be unacceptable to you, his model girlfriends are influencing him, or he's gay, either way, it's not good.

The way you describe him, is somewhat unsettling to me, as it doesn't seem like you feel you are equals, and that is a huge red flag. If you're not feeling like you're his equal, this will cause a big rift in a relationship. If he's that into his body, is extremely ambitious, thinks he's so much smarter than you, has to be surrounded by model-material girlfriends (another huge red flag), and hasn't an ounce of humility, that's a huge turn-off for me, as an ego like that can be deafening and isolating.

You say, "I definitely do not want to leave because I love him more than anything and we work really well together as a couple. He's always stressed about something and he never seems to think about having sex as a way to relieve that stress. Maybe this whole problem is my own insecurities about not being as intelligent nor as attractive as he is. His past girlfriends and his friends who are girls are model-level attractive whereas I feel like I'm very average. Cute, but average."

This is not a good basis for being in a relationship, I'm sorry to say. Your level of insecurity will diminish with time, which will feed and grow his ego. Why does he have friends who are all girls who look like models? Again, I'm sorry to say, but none of this sounds healthy to me, and perhaps you're not looking at your relationship in a balanced and healthy way, if you place him on a pedestal, and think you're insecurity is the reason for the problems. He sounds like an egomaniac, to be honest, and I'd assess your reasons for being with him.

I wish you well.

Sounds like it may be stress. Us as women, (or at least me, lol) see sex as a way to fight stress... but stress makes a lot of men not even think about sex. Have you tried anything different? Maybe sex is becoming "routine" Either way, He should be working to fix this, just as much as you. As they say, it takes two to tango. I wish you the best.