Once they have announced they are through (or not in love, or want a divorce) they consider themselves "free" to pursue others, even though they haven't done anything practical to get divorced yet.
And you are right, the novelty of infatuation temporarily trumps the familiarity of a steady relationship.
He may or may not turn around - but the path you follow remains the same: WORK ON YOURSELF.
Confidence is attractive. Clinging is not. The more you focus on getting a life for yourself, being all that YOU can be, the more likely he'll notice and be interested in you. And if he doesn't come back, the better off you will be for your future adventures.
What have you always wanted to learn to do? What challenges have you ever dreamed of tackling? Now's the time! Climb a mountain? Learn to play drums in a rock band? (I've done both!!! )
Whatever it is, now is the time to pursue your dreams. Get busy with your own life. Take stock of yourself - do you need to lose weight, firm up, change your hairstyle, try new clothes? Let loose a little.
And if you find it unacceptable that he is flirting with other women while living with you, feel free to boot him out. It's okay to stand up for yourself and set limits - odds are he'll respect you more for having a spine. Just don't shoot yourself in the foot financially - make plans. If you can't afford for him to move out yet, bear in mind that while he's still living there, you have more opportunities for him to see your changes. Go out in the evening and come back late - let him wonder where YOU have been for a change.
And I second the previous advice, gather all financial records, check your credit cards, make sure he's not running up debt or raiding savings accounts. If you decide to boot him, consider taking half of all checking and savings and transferring it to your own account before you tell him.
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