Why do i get jealous of my boyfriends habit?

i work full time and he doesnt work right now, but everyday when I am gone, he looks and gets off to , if i leave to go anywhere, he gets off, atleast once a day, doesnt do it when i am around, told me he still thinks I am attractive....says he just likes the actions, its not that i mind , but sometimes i feel as if it replaces me. hes been gone over the weekend at this clinical study, and i have to pick him up minday morning, he hasnt been able to get off at all there, and i always like to get him off when its been a while. but monday I have to pick him up and drop him off and go to work. so my thought is "damnit hes just going to get off to , maybe i can give him head on the way home" I seriously dont want to be jealous, but it just happens. how would u deal with this. I know men rarely change. I am not asking him to change, but for me to get rid of my feelings. We have been dating for 3 years and we are 23 and 24