There's a few things to look at when it comes to relationships. Unfortunately, no one is given a book or instructions on relationships, so most of the time we just sort of wing it. When you first meet someone, and decide that the two of you like each other, then you start spending time with each other and doing things together. After a certain amount of time, you'll want to talk with them and see what they are looking for and you can tell them what you are looking for. Now if what you want, and what they want is similar, then you both can decide if you want to go further, and if its not similar, then you still have to make a decision to move forward or let it go. Preferably, this is done before becoming intimate. Unfortunately, people are not always honest, additionally having sex can change peoples minds as well, if they are not sexually compatible.
When he first asked if you were looking for a boyfriend, regardless of the reason, you said no. Now that you've grown closer to him and have changed your mind, it doesn't mean that he has to change his. As women, the more time we spend with someone, the more we become attached to them, with men, this isn't always the case.
He's basically told you that he doesn't want a relationship, he's not looking to get involved emotionally, that this is just fun and games for him, and that if you want to stop, then you are free to stop. So at this point, if you don't stop, you still can't expect anything more from him, because he's already told you what he wants. I have more respect for someone who does that, than someone who calls themselves your boyfriend, while dating others. I'm sure he likes you or he wouldn't be intimate with you and be around you, but the question is, does he like you enough?
Does he like you enough to give you what you want out of this 'relationship'? If not, then you are taking a risk of still sleeping with him because when he does come across someone he is interested in having a relationship with, what's going to happen to you? Or what if he just decides to move? Or that he just doesn't want to sleep with you anymore? Then what? The longer you sleep with him, and he won't commit, eventually you are going to wind up resenting him for something he was honest with you about from the beginning.
If you are looking for a man that will commit to you and be there for you, then this is obviously not the man for you. If you are looking for someone to fool around with, and just keep it as friends with no ties to you, he's saying he can accept that. The question is what are you looking for, and will you allow what you're looking for to come into your life or will you stay with this for now?
I welcome your thoughts, let me know if you want to talk more