It's low self esteem Indi. I know people like this. They implant in their heads this ridiculous idea that they will never be able to find something better than target x because of their perceived low value thus their only choice (and purpose in life) is to pursue x in any way possible. They will take as much punishment and humiliation as x is willing to throw at them without any boundaries or internal standards until such point in time where x gets tired of walking all over them and leaves of own accord for something perceived as better leaving their partner completely oblivious as to why this has happened.