Birthday or cheat day😒

My boyfriends birthday is coming up in February and he has this tradition with his boys where they'll all get together and leave to San Diego for the weekend it'll be the 2nd birthday I get to "celebrate" with him. We've been together for a year and a half and last year I didn't really feel the right  to say nothing just because things were barely getting more serious. It did bother me but I got over it. And now it's being brought up again and now it kind of bothers me more because I've gotten to know him so well and we've had our bumps here & there that have lead to trust issues & now that I thoroughly think about it, I get to thinking that what if he's going out there to cheat & obviously his boys won't say nothing. He says all they do is "have good food & just go to a few bars" & that's it. My birthday however is the month right before his & im thinking of planning something without him just for the experience with my girls out in Vegas just to make it fair. I just don't wasn't him thinking I'm doing it on purpose because of how he wants to celebrate with just his friends. All in all it just makes me feel left out😞