> How can you possibly love someone when you know in advance that there's almost a 100% chance
> they're going to betray you, and think terrible things about you--particularly that your very
> existence is an impediment to their happiness with someone else? And they're going to think
> it while you're still loving them, and thinking that they love you!
This is probably why it's so much harder to fall in love as one gets older -- these experiences build up, too much negative conditioning. Get all curmudgeonly.
But I don't think of things as inevitably ending in betrayal. That is one way things can end, and probably the most horribly painful way, so that's the one I think is to be avoided by not being deceptive.
To have someone love you, and to have that love wane and vanish, I don't think of as a betrayal -- I just think people are complicated and things like that can happen. Just life. It is painful, and a disappointment and a loss, but it's not a betrayal unless someone has convinced you that they will love you forever. And that's the way it often happens. When I was younger, and new at this love stuff, I felt very much like I would love someone forever. It was thought and felt and said at the time, both by me and to me. But then it goes away, with someone else involved or not, and things go to hell and it feels like a crushing betrayal. But now I just see it as how people work sometimes; that love is a pattern that takes over the brain to a degree and deludes the afflicted into thinking all sorts of funny things. So those experiences and that knowledge make it almost impossible for me now to think or say that love will last forever. I can still be in love and feel that it will, and be hurt when it doesn't, but I just won't rationally believe it. And, personally, when I act or say things, I try to follow my rational thought as best I can.
So... I guess I have an existentialist view of love as something rare and complicated that happens in the moment, when it happens at all. It's to be enjoyed and lived, even if it is going to probably end in misery, or at least death, eventually. Such is life. So if anyone tells me, and even if I tell me, that I'm in a love that will outlast eternity, I believe that the feeling is there and is real in the moment, and isn't a lie in that sense, but that it's just probably a very poor prediction of how things are actually going to pan out down the line.
And thinking that about love, I have to think the same things about relationships. That it's a wonderful thing to be in one with the right person, but I have a hard time believing they will last forever, just from statistics alone. And this also tells me that it would be horrible to think of a relationship as an investment; because that would mean, when it goes, the whole thing is going to be felt as a huge loss, rather than as a gain of the wonderful time that was shared together when things were good. So, for me, if and when things do end, I don't feel betrayed and I don't feel I've lost my time to a bad investment; the only pain I feel is the loss of something I had that was good -- which is bad enough, but not as bad as it could be. And it doesn't make me bitter, just kinda cynical. Heh, kinda.
Which comes back to what it feels like if a partner is with someone else, which I think is what you were originally asking and I've been dancing around, but have now built up to. When that happens, all I feel is the threat and sadness of losing something good. I don't feel betrayed, as long as my expectations haven't been wrongly built up -- i.e. as long as I haven't been willfully deceived and lied to by my partner. And I don't feel a loss of an investment, since I wasn't in possession of anything. I really just feel the loss of a future of feeling good. Emotionally, of course, there can be painful images of a partner being with someone else, but those are mostly just torturous imaginings of what I'm not getting. And if it happens that a partner is with someone else sometime when I'm not around, but that when I am around and I want them to be with me, they decide that they do really still want to be with me and are, fully, then that doesn't hurt, since the present and future of affection are still there. It does, however, make me more wary of the threat that they won't want to be with me, or that I won't want to be with them, but I'm aware of that possibility anyway, being kinda cynical.
I think I'm mostly fantasy driven -- I imagine what I want, and try to make it happen. And it's OK to fantasize about being in a love and relationship that lasts forever, as long as you don't expect that sort of thing to last forever.