It's not a dumb thing. You were willing to work things out. A marriage is full of ups and downs and requires work and effort on both sides. I was with my stbx for 22 years and when only one person seems willing to work at it the marriage slowly breaks down. Her multiple affairs didn't help either.

Most importantly, do not blame yourself. Sometimes a relationship is just doomed to fail, nothing you can do. Consider yourself one of the lucky ones who didn't have to go through 20 plus years of hell. You found out now and you are young. You will see in time that this was for the best. You'll be better off. Yes it hurts and the feeling of rejection is a pain I know all too well.

Look after yourself, put the focus on you and shift it off of him. Stay strong
-HUGS-

It's so hard to tell yourself it's for the best when they're the only person you want. When you don't want to even bother trying to find another.

Grieve. It's a part of healing. Don't jump into another relationship right away. You'll be only trying to fill the void in your heart and may lead to the same problems down the road. Heal yourself first. Therapy and counseling will help, which I do recommend. You don't feel like it now because the wound is fresh. In time, you will feel better.
-HUGS-

Since you can't control what another person is thinking or feeling or behaving, it is best not to beat yourself up over anything he says or acts. He had no business involved in that level of commitment and thus the fault was with him and regrettably you are paying the price for his short comings. Definitely don't jump into anything or ever consider allowing him back into your life...he will only make you miserable.

I'm also in a puddle of misery right now. Try to hang tough. We must all push through the darkness to that blissful light

It would be very unrealistic to want another guy in your life right now. You need to give yourself time to learn what went wrong. If he thinks you're full of shit, where that came from. What contributed, from your end, and from his end.

Takes ages. Him blocking you is the best thing to do. You blocking him also would be very healthy. You guys need space away from each other to process all the stuff that has happened.

This wasn't your fault and I agree with everyone about living by yourself for a while. He's shown you his true self. Believe him.
Living on your own for a while will teach you a lot about self worth and what you really want in your life. You need time to grieve this loss and pick yourself up and move on. There is a certain feeling of self worth knowing you don't NEED a man in your life. To want a partner but not need a partner . When the right one comes along you will know he's the right one for you.

Just a thought and sorry if I am harsh: if this were the life leading up to a marriage, imagine what the actual marriage would actually look like...