Trigger warning: sexual assualt

I may have been sexually assualted when I was sixteen. I'm 21 now and I still don't really know what to call it. My boyfriend at the time started going further than I wanted to while we were kissing and eventually I said, "we should probably stop" but he said "why?" and continued. After that we continued to fool around. I don't know if this is sexual assualt. I wasn't ready to do what we did at the time but I just thought it was typical sexual pressure. I'm starting to realize it may have been something more. I want to tell my mom but I don't want her to see me differently or to feel hurt and burdened by this news. I don't know what to do.