He sounds like a complete and utter tool. He probably thinks he's smart making facetious jokes about your weight, that's just not appropriate especially when he knows how insecure you are about it. And the flirting with his housemates is terrible too, that's probably him trying to boost his ego seeing how many women fancy him (trust me i've been there). He probably doesnt mean anything by it, he just enjoys female attention, and who doesnt but if he takes it too far, i say you ditch him on the spot. But before all that, it all boils down to one option. Talk to him, tell him you don't like him flirting about with other girls, if he's got time to do that then surely he has time to spend with you, rather than letting other girls inflate his pompous head.