People who don't have a romantic partner might complain about being lonely. And after finding someone, they may then complain some more, about the problems posed by the relationship. When you embark on a relationship with a partner you might be exchanging one set of problems for another.
Romantic type relationships, including cases of unreciprocated attraction, invoke some of the strongest emotions that people normally experience. Jealousy is one of these--and it is not the prettiest one.
When someone suffers from a severe mental illness and then gets into treatment, handling the emotions, the demands, and the responsibilities of a romantic relationship can be overwhelming. If someone with mental illness is emotionally underdeveloped in that area and isn't quite ready to handle a relationship, it doesn't mean that the person will not seek a relationship.
Seeking or going into a relationship when unready can be destabilizing--for people who initially are just trying to keep themselves intact.
Over the past thirty years I have been in some relationships that have gone south. Some of the situations didn't work because they weren't mutual, while others were with someone unstable, while still others were with people in a different place than I in their development, either farther along or less far along. Thus, when I met the person who would become my wife, I had some amount of experience under my belt, as did she. We ultimately both realized that we were and are right for each other.
Not that my present situation is without problems. However, we are both willing to work at it. I believe I am reasonable and am dealing with someone else who is reasonable. And we have some amount of "chemistry" which is part of the glue that holds us together.
I would say that if you can not behave decently and fairly toward someone, you are not ready for a lasting relationship. Part of this includes acknowledging mistakes. Part of it includes forgiving for someone else's mistakes. Part of being in a relationship is the willingness to compromise. Yet you do not have to be a human doormat.
To behave oneself, a person must have some amount of mastery over that lizard brain, the primitive part of the brain which lies underneath the cerebral cortex. If you don't have that, then you are doomed to be controlled by immature instincts. Since becoming mentally ill, nearly all of the relationships I've had have been with other people with mental illness. This is both good and bad. It poses problems because I am dealing with my mental illness and the symptoms of the other person. However, the good thing is that my disability can be understood--and it is not a source of inequality. If you are dealing with someone mean and nasty, someone who is addicted to illicit drugs or alcohol, or someone abusive, you are dealing with the wrong prospective partner. You can not fix someone else. Furthermore, one should realize that predatory people tend to lie and to promise great things--the observable facts don't match the talk. I have been in job situations, for that matter, in which I resented the manner in which I was supervised. Employment is also a type of relationship. In either category of relationship, if someone can't treat me well, I'm not going to stick around. Being able to skillfully break up if something isn't working is another asset. This was something I learned the hard way. I'm not a relationship doctor, and all I can offer is a little bit of common sense. Getting through a few bad situations and remaining intact may be a necessary experience before finding the right person. Sometimes the right person is simply someone with whom problems can be worked out, and not someone with whom you think there won't be any problems. If things are sometimes difficult yet workable, it might be that you have found the right relationship.