Can't get over boyfriend's ual past?

i dated him for a year and 4 months, he has an ex gf, and i have ex too. but i nvr do anything with my ex, just kiss, but he and his ex get naked together, and he even fingered her before. these thoughts are making me crazy, and jealous and it's torturing me. like when we have , sometimes i would think if he touched her like this too something like that. i love him so much but i want to get over this or else it will ruin my relationship when i always talk about this to him. he says it that she is nothing to him anymore and that he loves only me. the thing is i am jealous of what he did with her, but i am sure he wont go back to her. i am just jealous he had been that intimate with someone else other than me. HELP