My experience of love is as a state of being, not dependent on external factors, and I agree there are different types of love, but I'm not looking to get into that.
I think you're going to have a hard time experiencing love if there are 'shoulds' or ultimatums attached to it, because passionate love, by its very nature, pushes your boundaries, confronts your comfort zone. As was mentioned above, one needn't be a doormat because of their open heart, but one doesn't stop loving in the face of difficulty either because the act of loving is itself the means and the end. I love for myself in other words. If someone's a dick to me I'm not going to stick around, but I'm not going to close myself off from loving either, because its not for them, its for me.
This is, as with most matters of the heart, easier said than done. Furthermore I'd be lying if I said this is a state of being I have much access to, but it's not just reciting what I read in a book either, I've been there, and it was fucking fantastic. Imagine your life on fast forward ×20 and you're still not there, but maybe in the ballpark. I've said it before but its gotta be comparable to living like you're dying. Read something from t mckenna once after he'd found out he was done for, and one of the things he said was how surprised he was at just how in love he was with even the simplest aspects of life. Its like the difference between babying a brand new car around potholes or being chased by the cops highspeed down the freeway offroad and over road spikes and speed bumps, crazy sparks and shit shooting everywhere, because it doesn't need to last forever anymore, just a few more miles, like the point of life becomes life itself, to experience it as much as you can before your body craps out on you. Yeah, something like that anyway.