What is a relationship?
I saw a police drama on TV recently, entitled 'The Commander', with Amanda Burton as the eponymous central figure, which may shed some light on this question.
Amanda Burton was clearly a role model of the ideally good person in modern society, but she started to have a relationship with an ex-con who had committed some murders in the past and was clearly a bad egg, since he was white and middle class with intellectual interests (described as a writer), in contrast to another suspect for a recent murder who was black, working class and so inarticulate as to be scarcely comprehensible.
So far as I could see, in his interactions with her, the middle class guy behaved as well as would be expected of anybody in such a situation, and she was getting the sort of emotional feedback out of it which she wanted to get. If she continued the relationship with him after he had become a serious suspect for more recent murders, that would seem to be her fault, not his. But when a police colleague, in the approved modern style, spitefully spilled the beans about her to the tabloid press, so that her career was endangered, she thought it right to do the dirt on her 'relationship' partner as soon as possible.
She went to his flat armed with bugging devices and lured him into bed with her, setting what I believe is called a 'honey trap', telling him that nothing turned her on so much as knowing that she was sleeping with a recent murderer, and reminding him of things he had said about doing anything for her, and trusting her with anything. She really wanted to know everything about him so that they could be really close.
Then, it is true, he tried to kill her with a plastic bag, showing how much residual inhibition against harming her the 'relationship' had left him with. But he was a bad egg anyway, whereas she was the role model of politically correct upright behaviour.
So it is really not clear to me what is supposed to be implied by a 'relationship', except that it seems to justify either party, but especially the woman, in ruining the career of an erstwhile partner, damaging his car, cutting up his clothes, etc, if he starts to have a relationship with anybody else, or falls foul of her in any other way. (E.g. Blunkett's ex- lover, who has ruined his career by spilling the beans about his trying to do her a small favour while they were having a 'relationship'.)
Clearly a relationship does not imply that the parties concerned have the smallest interest in promoting one another's interests, or even that they would refrain from doing one another as much harm as possible.