http://curiosity.discovery.com/question/are-women-more-emotional-men
http://men.webmd.com/features/why-men-cheat
http://curiosity.discovery.com/question/are-women-more-emotional-men
http://men.webmd.com/features/why-men-cheat
"Don't ask a question if you can't handle the answer".
So he doesn't believe in monogamy but he's prepared to be that with you... for now. I think you need to have a clearer conversation with him to define the terms of your relationship, not all relationships are based on monogamy but that would only stand a chance of working, in my opinion, if those terms were acceptable to both parties from the start. It doesn't sound like he's asking for an 'open' relationship, nor does it sound like that would be something you'd be interested in if he was, so I think you really do need to revisit the subject with him and get a better understanding of what it is he's saying at this point, before you get more 'serious'.
Sleep is a symptom of caffeine deprivation.