I need opinions ( I didn’t know where to post it)

So there is this class mate of mine, during the whole month of may they were acting super weird.....they kept on touching my thigh under the table and i would move away because I wasn’t sure if it was my skirt but i looked under the table and saw their hand move away from my thigh as soon as i looked under the table ...they also did this to my close friend , and they touched her butt which we thought it was by accident ( it was before all of this happened). We are disgusted by it and the person. We have known the person since we were little so we don’t know what to do. Is it considered assault ? Or am i just over thinking this ? What should i do ? We haven’t told anyone because we don’t know what to do or how to approach it with the person since we have known them and were friends with them. Help.