you make my life suck

so, this is just basically me needing to get this out because i feel like i can't tell anyone in real life ..
my best friend and i have been hooking up lately. and usually just fooling around. we had sex twice, but idk. just like short sex? because he didn't have a condom. but yesterday. well yesterday i was at his house, because i just did NOT want to be home. so we were hanging out, and then we were fooling around and we decided to have sex. so, we started doing it. and at first, it was great.
but then i kept thinking about my ex. about how the last time i had had sex with him, i didn't want to. the last time i had sex with my ex i told him to stop. but he wouldn't. and i cried while he kept going. until he was done. and he left. he left me there.
all i could think about was my ex. so i told my friend to stop. he did. then i started crying. i was bawling my eyes out. i pulled my pants and and just curled up in a ball and cried. he didn't know what to do. he just kept saying that he was sorry.
i had told him before we started fooling around "the next time i have sex, i'm going to break down and cry" and i did. i just felt like i was being taken advantage of. being used. i couldn't do it. and i don't know if i ever will be.
i don't know what to do ..