PLEASE HELP, I’m so conflicted

idk what to do. Me and my boyfriend have been together for some time and we have intentions to stay together and get married, like we even live together currently. But...he keeps bringing up that he wants our relationship to be a bit more open because we’re in high school and about to be in college and he wants to be a bit wild and more care free when he’s out partying and if he does have sex with someone he doesn’t want it to affect our relationship and he’d want the same for me. I want him to be happy and especially cause we’re in a rough patch having a break where he could do whatever but then come back and have a fresh start could be nice ? I guess, but like I really don’t like the thought of him with anyone else at all. Like I know mentally it’ll make me worse and I’ll become more insecure and sad and I don’t know what to do. Like what’s a middle ground or something so that we can both be happy ?