need advice -- sexual assault?

i'm needing advice on a situation i've gotten myself into...i have a friend (just someone i used to work with) that i occasionally hang out with--just watching tv, etc. (nothing sexual) and i bumped into him last week after not seeing him for several months and he has come by to hang out a couple of times. so he kind of started to take it to the next level and i didn't really want to go there but i guess i wasn't putting up that much of a fight (we had been smoking weed so i was more than a little stoned) . so we end up having sex (rather he had sex) and that was that. i wasn't happy about it and felt like he had taken a little advantage of me because i had definitely said "no, we shouldn't do this, etc.".
so today he comes over and i had wanted to talk about it all--just to say it shouldn't have happened and be quiet about it...well he ends up completely overpowering me and despite the fact that i was repeatedly saying "no, stop, etc." he held me down and was rubbing, touching, etc and ends up (i can't think of better words to describe this) trying to have sex with me from behind...doesn't actually get in but cums and everything. i was really uncomfortable about the whole thing and just really didn't know what to do. he acted like nothing waas wrong, which made me think that maybe it wasn't that big of a deal, etc. i know 100% that i was trying to stop it and fight my way out but...what does that mean? i know i shouldn't be hanging out with people like this...i think i'm just a little lost in my life right now and somehow individuals like him have gotten into my life. just to let you know, i'm not some druggie from a bad background or anything-- i'm educated, come from a good family, etc. maybe that's why i keep telling myself that this isn't a big deal, like could this have really happened?