this is a hard situation to be in. You could just ask him but if he says no that would be awkward as you live together. Maybe slowly flirt with his and see how he react. If he knows you love him ask him what does he think of you?. You can ask his friends because he might have told his friends, ask him but avoid using love or words like that because that will put him off. Ask do you like me or something like that

You're having sex with your mother's boyfriend???

I think she means her mothers boyfriends son, and it is a tough situation. One thing I discovered though, was that sex can make things more complicated.. I think that right now, if you really like him, you should try to stop having sex with him (if you still do it). Sex a lot of times is driven by lust, not love, and it can ruin hopes of something developing. I learned that from experience :p from this it sounds like he likes you, but the fact that your mother and his father are dating probably scares him away.. still, instead of sex, try to do other things that may spark his interest. If he is scared of the situation like it sounds like, and you wanna date him, then you have to keep sparking his interest until he cracks..

Just a few of my thoughts. Sorry, I tend to ramble sometimes so I apologize if some things I said seem unrelated to each other.

Firstly, I believe the sex should stop. Build trust and confide in each other. Don't ask him if he loves you. Just continue to be nice. If he does, he'll eventually let you knw.