I'm in my mid-30s now, but when I was in my early 20s I had a few boyfriends who were in their 40s and felt much like you did. I didn't want to hear anything about my boyfriend's sexual past. As I've got older, more experienced, and more sexually confident, I've chilled out about it a lot and now I really enjoy hearing about my partners' previous sexual experiences. So I think it's something that improves with age and confidence.

Personally, I'm still attracted to almost all the people I've dated who I had good sex with, and I do occasionally reminisce ;) Different people turn you on in different ways after all. I also do look sexually at other guys even when I've got a boyfriend but - crucially - I'd never do anything, even if the opportunity was right in front of me (which has happened). Without knowing your boyfriend it's hard to say, but I wouldn't be as quick to criticise him as some people in the comments.

This is something to be open with your boyfriend about. You clearly need reassurance that you're sexually exciting to him, and that you're his number one. Feeling special is the key to feeling safe in a sexually charged culture. He's chosen to be with you after all, which counts for a lot. I think it's reasonable to ask for that reassurance and (if it's what you want) not to hear about his past experiences. Good luck :)