Love can kill you, easy. She hides behind this veneer of sacrifice and selflessness but in reality she’ll take everything you have to give without blinking. And tell you not to be a monkey about it.
You become selfless because you don’t have a self anymore. You start to care more about this person than you care about yourself, than they care about themselves. What their dreams are. What their plans are. What their favourite breakfast is so that you make it in the morning, slavishly, whether they’ll finish the whole plate or not.
Not that being a slave is necessarily a bad thing; maybe everyone should be controlled by something bigger than ego. But when you don’t know you’re a slave, it’s almost as bad as if you find out that you are, at the end of this sentence – and then continue.