May I suggest the question: 'So - have you got a girlfriend?' If he starts gushing on about some female, you've got your answer. If he grunts a negative, the follow-up 'What about a boyfriend?' MIGHT be possible in these politically correct days.... depends on your local culture.... and again you will gain a lot of information by how he reacts to the question.

But on the whole I would be amazed at the idea that there is any sexual attraction on his part if he's been sleeping in the same bed with you but never tried anything.