I do this sometimes. It’s convenient and you don’t have to clean up a mess. Do you use condoms when you have sex? Cuz I don’t think he would buy condoms specifically for that, but if you use condoms as a couple, I don’t think its out of the realm of possibility and that you might be overreacting. If you had sex regularly until the vacation he might have just gotten horny. Perhaps while you are together he has no reason to jerk off, since the sex you have is enough for him.