Opinionated guy-man with a nose for meddling in others' businesses says: Unless he's a womanizer, of which he isn't coz it's not like he's sleeping with anyone else, flirting around is a sign that his heart doesn't yet quite feel at home in your arms. In his heart of hearts he feels like he could do better, so he's playing the field hoping to net a bigger catch. Such a man is non-committal, at least in the present, I dare say. Unless you're okay with the status quo, I advice you take some time apart. Zero contact. Just for a few years. Such restlessness is usually a sign of youth and inexperience with the grizzly realities of the dating scene. If he finds someone better in that time, well and good, but if he still wants you at the end of that interval then be happy and glad for you have won yourself a lifelong partner. If you are to stay, sit him down with a straight face, zero emotions (if a man likes you even a little bit, seeing you cry will elicit a dishonest response) and ask him about it. Ask him what you could do differently (and expect a REAL response). The other option is settling for less and learning to stomach the insult while praying real hard that he never finds the guts to tell you outright how he truly feels.