I need help

Hi all,I am gay and I have a boyfriend for almost two years now. I had my first everything (kiss, sexual experience with my current boyfriend when I was 21). I am just having some problem accepting where I am (in life right now). For example, I got bitter all the time when I was outside seeing other gays. They always look like they're having a good time. I am pretty happy about my relationship right now but for some reason I am bitter about how people get to have more sexual experience than me. I always fantasize about hooking up with other gay men, but I'm in a relationship so I'm keeping myself away from doing that. I love my boyfriend. But this human part of me keep me wanting to have more. I'm 23 currently. Just for further information, my boyfriend agree to my proposal of having occasionally threesome so that kind of keep myself satisfied. However, we have very different preferences when it come to guys. So sometime it doesn't work. I am really frustrated and would like to hear some feedback from you guys. I know I am asking too much but I want the best for my boyfriend and myself. I'm in my twenties and I don't want to waste it.