Why don't guys like talking about past crushes and relationships?

Girl.. well first off if you can talk about it and laugh about it then you are completely over it right] like can't you laugh about old memories that you did or lame shit that you used to do that mean you accept it. If he's trying to ignore the subject he's either hiding something or doesn't want to tell you something happened or he ain't over it ] I used to do the same shit way back then but I mean he will learn and yeah the reason why I never told my boyfriend about my past is because I was embarrassed but as time flew by I let it go and accepted my mistakes. yup

Because whatever happened in the past is the past. Girls have a way of getting information and storing to use as ammunition later. That's never anyone's intention, but rest assured there will be an argument and something will slip out like "No wonder so-and-so dumped you!".

You're young still so it's possible he doesn't really have a long roster of relationships to discuss...

If it makes you feel any better I don't know much about my husbands past relationships, just that he doesn't have any STDs or kids. The rest is still somewhat a mystery. And I'm ok with that.