they shouldn't put up with somebody if that person isn't making them happy. and as owl said, it's natural for them to feel like they don't need or want help. they might feel like they'd be bothering you wanting your help, they would become inferior if they had to rely on you, etc. but i think it's important that you care about your friend's happiness and do whatever you can to make their situation better, even if they refuse your assistance. just don't completely get rid of their boyfriend/girlfriend at first, because that will only make things worse.