I'm confused why he would let his dick size bother him when it's a really good dick.
Because you yourself said it wasn't a good enough dick.
I'm absolutely unconcerned about my penis size, but if my girlfriend told her friends that, quote "the only thing he is missing was a big dick like my ex" I would kick her to the curb.
I'm pissed at him for being that insecure and not talking to me.
He's not insecure. You have behaved fucking horribly:
You thought it becoming to denigrate his body in front of your friends, making him fit game for laughs. If you think this is fit behaviour towards someone you love, you're off your chump.
You thought it becoming to do so in a field where everyone - man, woman, young, old, is most vulnerable: In their shared sexuality with someone they love. Again, if you think this is fit behaviour towards someone you love, you are developmentally stunted.
You thought it becoming to throw your shared intimacy to your friends as one throws a carcass to the hogs. If you think such a breach of trust is fair game, you don't need to be in a relationship.
You promptly moved on to shift the blame onto him and to obsess with YOURSELF: "I'm pissed", "I'm upset", "I'm jealous", "I'm hurt" - I I I , MY MY MY, ME ME ME, NOW NOW NOW!
And all this you did to a guy who "'s absolutely what I want in a man". It makes me shudder to think how you behave towards other people then.
didn't even know this could be a dealbreaker for guys.
Really? If he made sport of telling his friends you were great and all, "the only thing you needed was a tight cunt", you would be fine with it?
No, don't answer, I don't even need to hear the cringing lies :D
I don't know how to fix this.
Learn to not be a terrible person, try to pick up some delicacy, empathy and, oh y'know, regard for people who aren't you along the way - and better luck next time, honestly.
I want him back. I don't know what to do.
Reflect on how nauseatingly shabbily you behave with him, grovel for forgiveness on your knees and hope to god he takes you back, and if he does work on your behaviour at the speed of light.