How can i prove my boyfriend wrong?

So me my boyfriend have been dating for almost 3 months.
in about a week it will be. this other guy I liked. I had a thing for
during summer. which EVERY girl likes him. but I dont anymore.
I saw his face I thought he was ugly. lol. cause he got...

his
hair cut. but my boyfriend always says stuff like im sorry im not
as good as him im going to try be better. well I always
tell my boyfriend he is way better but he keeps doing it. what can I do to
like make him understand?

tell him to shut the f**k up and grow up, it id for attention, if you give it to him straight he will realise he is been silly.

He sounds like hes got some insecurity issues. Your with him, that should be proof enough?

He only feels threatened by him becos you made him feel insecure. Now you gotta deal with it. The only way he'll be able to ease up and forget about this other guy is if you stop talking about him, dont pay any attention to him, and your boyfriend starts to feel how much you care for him, not the other guy, and he will eventually grow tired of mentioning him himself and get over it.