was this sexual assault?

so there's this guy that i kind of used to flirt with a while ago. but he got a girlfriend and I've been talking to someone so we stopped. I'm 15 and he was 17 when we first met but he recently turned 18. yesterday, he came to study with me at the library and everything was fine until he asked me to help him find a book. he took me to where nobody was around and he kissed me from behind. but he had one hand around my throat and the other wrapped around me so i couldnt pull away. then he kept doing things like shoving his hands down my shirt or pants while i was trying to walk away and telling him to stop. towards the end, he wrapped one arm around me and was holding me still and had his other hand between my legs. i tried pulling away and i told him to let me go and to stop but he just said "you know you like it" and kept going. i cried alot about it but idk why. am i just being dramatic over this or do i have good reason to be upset? and did he just think i was joking and thats why he didnt stop? my friend said he sexually assaulted me but idk if shes right