Do i beleive him?pls help!!?

I was 17 and i just want to know if what my dad did is sexual abuse..me and my parents were holidaying and we had just one room and one bed and so me my mom and dad shared the bed with him in the middle..at night when we were sleeping he started stroking my thights and kept on stroking my legs going higher and higher..i woke up but pretended to be asleep coz i couldnt beleive what he was doing and i was really scared...i pretended to be asleep and i moved away from him..he moved closer to me and kept doing this ..i am really scared ..he did this when my mom was in the room so i cant imagine what he might do when my mom isnt and next day i was crying and my mom was out so he knew that i knew what he did so he wrote me a note saying i must never tell my mom and he is not as strong as i think and he has problems and i should behave like a big girl now...he keeps asking me to forgive him but i dont beleive he wont repeat this i am scared of him..he has kissed me on the mouth before and he has touched himself in front of me and keeps puttin his hand in his pant when i am there in the room...this was all before this incident...i dont trust him...now i am 18..i told my mom..initially she was very angry with him but now she talks to him and behaves normal with him...he says he has changed and he is sorry...i dont beleive him cz he has not gone to any therapy ....can i trust him?