My sister's boyfriend tried to kiss me

My sister's boyfriend (shes 17 and he's 18) came over to my place to watch a movie with her. I (im 16) was watching it then he put his arm around well my sis was in the bathroom and he even to kiss me. I tried my best to push him off but he was too strong. Than my sis came back and she was furious with us. She yelled at us then kick him out. She ended it with him and was in her room crying the whole night and wouldn't come out.

I admit I can mean to her sometimes but I'll never do something like to her. What should I do? I talk to her about it but she'll tell me f*** off.