I think it's all very much relative as Cogito says.
I've only had short relationships really, ever. Nothing longer than four years, well, maybe a bit of to-ing and fro-ing after that iyswim, but anyway, mostly it's been a few months and they've been unhappy from very early on.
And then sometimes I'd be trying so hard with my head to justify and rationalise all of it, because I thought the person would make a decent partner on paper, and actually, I wasn't really into them at all.
You only see the difference when you meet someone youre totally into in a massive way. Then the time seems to go really fast and suddenly you've been together a year and you hardly even noticed. Because you're always just living, and looking forwards.
I think you can fall out of love, well almost, but someone you love that much you won't ever really stop being in love with just a teeny, tiny bit. Even if cognitively you can't stand them. The attachment remains because you have something very strong between you in terms of being similar, understanding the same things, etc etc. That stays the same.
So heartened by this I do now believe two people can be in love all their lives, whereas before, I don't think I really understood this.
I can see now that had I settled for one of the men I thought might be 'alright' for me, without the big love thing being involved, I'd have been missing something hugely important, which in the end, just comes along and happens to you if you keep waiting.
I don't imagine falling out of love with DP for a very long time. If ever. I mean, who really knows, but it's in the present, really in the present and that means it's working RIGHT now, not 'if one day he did this' or 'he could be really great if such and such changed' or 'I think I am starting to like him'. It's just full on, immediate, 'this is it so hold on tight!'
And if one day that stops it will still have been worth it. You sort of don't get a choice...if that makes sense!?