I think my bf is jerking off at work..

Now I don't know for sure but I think he is masturbating at work.. My bf doesn't last long anymore, maybe a minute if that.. A couple of weeks ago, I for some reason made a joke about him doing it at work, and he got super weird and stuttered a bit, which made me think he was, but I thought no way. Now this was the first time I thought it, then I start noticing that about 2 months ago he use to text me everyday, while he was in the bathroom pooping, now never.. ( now that may not mean much, but a daily routine that changes, in a locked bathroom with nobody even on that side of the building, weird to me.) Now we only have sex like once a week, his choice.. And I'd notice some days he can't get that hard, or he would last longer which is weird since I haven't had sex for over a minute but only a handful of times in eight months or he should be super horny since we only have sex once a week and he's only 24. And he's never really horny anymore. Now I know for 115% he isn't cheating ladies. What do you guys think, I wanna say something because our sex life really needs to change, I'm not pleased at all but I don't wanna say anything cause its really hard to talk to your bf about how bad his sex is..

For everyone saying he's cheating he's not. I know as I said for 115% he's not. I asked about him jerking off at work, not for him to accused of cheating. AS I SAID HES NOT CHEATING!!!! so please dont put that as your response.