insecure

I’ve been with my boyfriend for some time and he has never given me a reason to not trust him or think he is unfaithful. We are both in separate colleges about 40min away. We have a good relationship but why is it every time he says he is going out i get this pit in my stomach? I don’t ever bring it up because i feel like it will just creat unessary problems if it’s just me being insecure. I don’t want to seem controlling or make him feel bad for going out with friends but I want to stop having this feeling what should i do?