<human>: So not a throwaway, but Im in love with lets call him S. 

So 6 months ago my parents kicked me to the curb, and I had nowhere to go. S&K( my exs parents) took me in as their own child. K always treated me like a daughter, she always wanted one. And S, well I always thought he was attractive but never really acted on it, he was a dad to me.

Cut to last tuesday. I moved out of their house at the end of september but I regularily go over because Im considered family over there. I go to the house and only S is home. K and her other two sons were out and about. So we are just sitting on the couch and S asked me why I still slept with his son and what not. We keep talking like this and then S tells me that he cheats on K and they have an open marriage. He says he thinks it would be nice to have sex with a 19 y/o who he knows wouldnt say anything. Me. He says he misses me living with him and that he doesnt love K.

I love K like a mom and yes I do want to have sex with S, I dont know if I could live with the guilt. Shes more my mom, than my real mom is. 

What can I do?

Summarize the given text in a few sentences.
<bot>: My ex bfs dad cheats on his wife and has hinted he'd like to have sex with me. I want to, but not sure what to do.