Sometimes, we're already aware that the relationship is getting toxic. But we end up justifying everything, finding holes that will give us a little light. To see goodness in every worst crumbs of it. We can't blame them! We choose them over ourselves, we destroy ourselves in the process of making them whole. --- It wasn't love at all. I don't exactly know what it is called. But I know, it wasn't love. 
I know this dynamic. The word for it: sacrifice. See I used to love others just as you describe. I thought that if I gave enough of myself, even at the risk of harming myself, or even less sinister, just putting myself in the back seat so I could cater to and take care of my partner--I thought doing that was a way to love someone. I thought like Christ, giving a great sacrifice was a display of great love and maybe for God--that's what it was, but for me--it's just sacrifice. It's just me pretending to love someone else more than I love myself--that is impossible. It's was just me equating sacrifice with love and they clearly aren't the same. Doing one will not bring the other. Love is love, it doesn't take away, it only gives. Love is big enough to give to yourself and those you care for all at the same time. Sacrifice is the game of choosing one over another. Sacrifice is sacrifice. Love is love.