Staying in “HARD” relationships

Why do women stay in relationships with people where it’s constantly up and down? Do all relationships really have to be hard & do we really have to fight for love in order for it to work? I believe that the person I’m in a relationship with should make me happy and make me feel secure .. I shouldn’t have to feel like my SO is a pain in the ass and difficult to deal with. To me that’s stressful and not worth it even if the guy is great.

I’m honestly asking for other women’s POV because maybe I have things twisted?