Do you think he is in love with this girl, and do you think he could leave my daughter and I for her?

WHY are you waiting for him to make a decision??? YOU need to get some backbone and get rid of this lying, cheating idiot who has NO respect for you and does not care if he emotionally hurts his child. I am guessing he doesn't want to pay child support, so he stays for that reason only. If you stay then you deserve it, kick him to the curb. Don't you believe you deserve better than that?