Because as soon as you don’t fight the end of the relationship, he wants it again. That is human nature (to want what we perceive we can’t have). If you are super-aware, you don’t do that — you are consistent and stick to what you say — but not everyone has that level of integrity within themselves (integrity meaning actions consistent with stated intentions). Most of us don’t — even though we try! And, since he is ambivalent (he likes or loves you but he wants his freedom to explore dating), his ambivalence spells a bucking bronco/emotional-rollercoaster for you — if you let it. You are doing great! Stay strong and keep focusing on your life. Stay away from the places that you might run into him right now. Look into joining a group (bike club, dance club, book club, gym?) that will bring you into contact with new people. Even a short trip away from your town will give you perspective. Do you have a good friend or family member you could visit?
Anonymous