If you're uncomfortable with meeting him, don't think it's a good idea but not sure why, it's your gut telling you there's something not right. Listen to your gut, most often it's right.

If he won't respect your decisions and your feelings it might be time to cut him loose completely, end all contact with him. He's showing his true colors by not respecting your feelings, your decision and that is a huge red flag.

I agree. Your sixth sense is telling you something isn't right. Trust your instinct.

Go with your gut..A relationship with many breaks and arguing is not a good sign. You say you have never met and have an uncomfortable feeling meeting him, then don't do it.

Your gut rarely lies to your head...unless someone is coercing you.

I think if you aren't comfortable with the whole situation, you are better off ending the bits and pieces you have.

Why do I think you don't want to meet him? A few ideas pop into my mind- you have told him lies about yourself? Haven't been honest about how you look maybe? You are already in a relationship and aren't "free" to be meeting someone else? You aren't the age you said you were? These are just my top guesses- are you going to tell us why you can't meet him or tell him the real reason?
What you can do is to stop communicating with this guy, if you have been flirting with him and basically leading him to think there is or could be more between you then you need to stop doing that. Personally I have never quite understood how someone can fall in love with you over the internet, they might enjoy chatting with you and want to get to know you better but I don't believe two people can have true feelings for each other when they have never met in person- it's too much of a fantasy sort of thing.
I am curious to know what is making you uncomfortable about him? Has he told you thing about himself that scare you? I met a guy online who seemed great but the more he told me about himself the worse things got. "I am divorced, I have two kids- two kids that I don't support, I live with my mother and 2 brothers, my brother has been to prison- served 11 years- umm ya me too I've been to prison several times, I have tattoos- prison tattoos- I actually look like Charles Manson... so when were you going to come down here so I can tell you in person how much I love you?" Safe to say I wasn't comfortable meeting him in person!
At this point you have two choices keep things as online only if that's what he wants, or end things if he is wanting more than just to be chat friends.

Just completely stop talking to him.

To me seems like you might be scared of things changing because you like how things are... either you or him might lose interest, or maybe afraid to take things to next level?

First of all, you really need to stop flirting with him! If you do, don't ask why he keeps bugging you. You are feeding his obsession and leading him on and that's unwise and unfair. You sound like you are giving him very mixed messages, which is just not a good idea in this situation. That will only feed any fantasies he has about you.

Perhaps it's time to cut the cord on this one, gently though. Very gently.

Also, you have to be honest with yourself here- are you keeping this situation the way it is because you enjoy the attention?

It sounds like both of you need to spend less time online and get out in real life and have healthier friendships and relationships. Four years is a long time to fight and obsess and flirt. Not good.

Is this an "online relationship"? If so, it ain't a relationship at all, until you've met and spent some time together in person.

Since you've already been fighting, even though you haven't even met in person, obviously, you don't want to meet him because you know from his writings that he's a dark, angry and potentially violent person.

Everyone's right. Trust your gut. If you're getting a dark vibe, pay attention to it. Something's not right.

Investing in someone for 4 years is a long time however when investing this time with someone online it's a whole different story. No matter how much time you have spent together chatting or skyping it doesn't ever add up to much considering how one dimensional this type of communication is. You can only get to know one side of a person (the perfect situation, edited side) therefore you can't know that person 100% which is why people want to meet. They want to take it to the next level, the REAL level. The reasons for your not being comfortable could be because you're not confident with #1 "him being in love with you" and #2 because then you're open to vulnerabilities i.e. he'll get to know you, where you live, work, etc. because then you'll have no excuse or computer screen to hide behind (which leaves it open to stalking territory). I think you're gut instincts should be honored and you should only do what you feel comfortable doing, however you can't go back to the way things were. Relationships and friendships progress therefore if you're not going to take things to the next level and he wants to then you have to stop leading him on. Let him know you're not comfortable with it and you're willing to do whats necessary to make that known. If he pesters you and continues to ask without your being ok with it then cut all ties and cut your losses. Again you have to make a change whether it be going to the next level, changing the way you talk to him, deleting your account, etc. You're enabling him to be obsessed with you and if he's investing time in you without getting anything out of it, it could be bad news. So again swallow your pride and make a change. Your interactions with this friend of yours has progressed to a point where a change has to be made. Good luck.