Yoyo, ping pong ball... that's me.

This particular male friend I've had for 17 years and I have discussed marriage but he's never asked me to marry him. He's been engaged to four women since we stopped officially dating but none of the relationships worked out. And when he's in a relationship he won't talk to me at all. When one breaks up he comes to me to talk, we start to get close again (no sex), and after a few months he finds someone else. He's asked me to move in with him, he hates living alone, but I'm afraid to since he has a past of moving people in, then after a while, finding a reason to kick them out. This man was there for me when my husband of 30 years divorced me. I've grown to love him more then I could have imagined, but I don't understand him. He has told me he loves me, but never having proposed and jumping from woman to woman, then back to me, confuses me. His past causes me to question his ability to commit. I'm in my 60's and don't want to spend the rest of my life alone and we've talked about this in depth. I even suggested a committed relationship and we stay at his house some nights and mine some nights, but that wasn't good enough. I've tried several times to cut him completely out of my life because I feel like I'm being used, but when he calls I tell him we can talk as friends and after a while the same old issues pop up. He'll eventually ask me to move in, I'll say no and within a few weeks he's with someone else. Right now he's been engaged for 5 months to a widow of 2 years that he's known for 25 years but never dated and lived with for 2 weeks before he proposed. Do I have commitment issues, am I being too stubborn or could it be trust issues. If he comes back again should I ignore him and cut him out of my life or should I give him an ultimatum? Any opinions will be appreciated... I'm not getting any younger.