is it normal to feel so much pain bc of my bfs past relationships

whenever i remember that he has been with other people (he is my first) i feel like i am being pushed through a meat shredder its so horrible . hes 21 and im 20. my brain tells me that he is always thinking of them even if i am right in front of him. he hasn't deleted pictures of them bc he said he "doesn't care about them even that much" but it just fuels the doubt in me .

 i hate myself and feel horrible every time. ive said to him before that even thinking about it, even the people he has just liked before w/o a relationship makes me sick to my stomach (literally i want to vomit if i think about it) he apologized before and doesn't talk about them any more but still drops info during conversation. i am a very sensitive and emotional person by nature. i try not to show it to him bc it will just make him sad but i just need to vent abt it because it just makes me feel horrible and dirty . hes my first everything while i am just the fourth to him. i hate myself