I saw my mom kissing another man (read the details)?

We were talking in the car wHere we wanted to go eat. She said pizza, suddenly she got a text and she wanted to go to a Chinese buffet beside foodlion. When we finished eating she told us to go to the car because she said she was going to get something, instead we went into FOODLION we looked for her and me and my cuz saw her kissing a man I know in front of my 3yr old brother. My cuzzins mom is my dads sister. I feel different towards her, now she grosses me out n I dnt want anything to do with her, but she's my mom. Any advise. Oh and she didnt even buy anything from foodlion. I'm thinking about my little bros future. I feel like beaten the shyt out of that guy. I AM