I caught my dad having sex with my mum’s best friend.

UNEDITED

AM 19, Last month I caught my dad having sex with my mum’s best friend. My mum wasn’t at home, she was at the hospital due to an accident while I was supposed to get her food that day, but I forgot to take some money COS I was supposed to buy milo and other things my mum wants, went back home and caught them having sex. Since that day, my dad has been VERY nice to me, he buys me alot of things JST 4ME NOT TO TALK but I do reject them. My question is, do you think I should tell my mum, I dont want my parents apart and secondly, maybe my dad and the other woman are still doing it. My mum is home now and feeling beta but am jst confused if i should tel her. Pls dnt Insult my dad, i know he Cheated BUT AM JUST HERE FOR ADVISE, THERE IS NO ONE TO TALK TO, AM THE ONLY CHILD.AND I LOVE MY DAD AND MUM SO MUCH. HELP ME PLS