My FI has a lot of "guys only" things - whether it is his guys' night every Thursday or the 5-6 college football games him and his friends travel for. I don't mind it at all. It is kind of annoying that none of his friends have girlfriends or want girlfriends, but I'm sure that will change eventually. My girls and I have girls' night every Thursday and we go to concerts, take trips to the beach, movie nights, etc..without the boys so he should have his time too.
I honestly think it makes us miss each other and keeps our relationship strong. I have dated other guys who didn't have or want friends and it was a bit smothering to me. I like having my people and he likes having his people and then it is double the fun when we all hang out
I wouldn't give up my girls' nights/trips for the world, so I can't say anything to him about his boys' nights/trips