Jealous...

I've been with my bf for 3 years. I first found out he watched porn like 6 months in and I got super uspet. I later realized that it's completely normal, and just a visual. I've been working hard on not worrying about it & have not cared about it for a couple months now. But this week seemed a little different. Even though we did it 3 times this weekend (that's the only time I see him)...it almost gets me jealous to hear him say he did it when I'm not there. 
For instance today he's been super swamped with midterms & training, so while we weee FaceTimeing he said he'll be back as he's gonna take a shower. 30 mins later he calls me back & says he took a shower & released his stress (aka masturbated) & now he feels refreshed. I'm like I said, I almost felt jealous in a way ? He told me I feel way better, to the point where I put him to sleep almost every time. Our sex life has been amazing these past 2 months, so I just don't want anything to change & I don't want to worry about this all over again. Any advice??