Why am I interested in open, poly or otherwise non-monogamous dating and relationships?

I've never cheated on a partner. I want to get this out of the way quickly. Have I thought about it? Yes, of course. The times I've really wanted to have been when a relationship was coming to a close. I wanted to see if anyone else was possible. I think this is normal for anyone.

I'm in my 40s and I've never had a normal LTR. When I think of the longest relationships I've had, I can think of 3. The first was definitely not the normal trajectory. We hooked up and I never left her house. I found myself coincidentally getting evicted from my place the day after we hooked up. It was a disaster. It was toxic. We argued constantly. I have since avoided dating anyone like this. I haven't had a toxic relationship since, but I also went a long time before finding another serious relationship. But I was certainly looking for an LTR. I would constantly find myself getting dumped as soon as I thought I wanted to make the relationship exclusive and more serious. The second long relationship was more recently. We dated for a year and never established whether we were boyfriend and girlfriend. Never had a talk and I just assume we were monogamous. Is that really an LTR? The third ended over a year ago. We started off by stating it was short term. Knowing that I didn't expect it to last a lifetime made it so much easier to just appreciate the present and what limited time we had together. It was wonderful. When she moved away we set an end date and continued dating until the day she moved. Unfortunately I'm still not over it. It had started to feel like an LTR. I wonder if she moved because it started getting too serious.

It just seems women get tired of me and leave. Nobody ever has anything bad to say about me. We just become friends. Perhaps I am just not the guy a woman wants for something long term. Nobody can be another person's everything. My ex was everything I wanted. I've tried dating, but nobody has all the awesome qualities I managed to find in my ex. I love my ex-girlfriend. I love my rebound afterward (didn't mention her before). I love my non-girlfriend ex that I spent a year with. It's almost like polyamory except divided over time. Serial monogamy.

I have accepted the fact that every relationship ends. I went through a few relationships accepting this. I think it's just time to move on from monogamy and let relationships overlap.