I think you hit the nail it on the head, 21%. It's not a matter of the one person NOT wanting to make the relationship work. It's just that it takes two healthy people and no amount of superhuman effort from one person can make a relationship function in a healthy way.
I understand the need to 1) Observe and self-doubt long enough to be sure that I am not just being oversensitive 2) Start notice underlying trends and commonalities between conflicts 3) Hypothesize about why those problems are there and exhaust every possible solution that could be personally executed.
However, at the end of it, there comes a time when you have to realistically consider whether the other person has the resources or the will to make changes. I am the youngest child in a spread out family, as well as the youngest of both sides of a large extended family and have had the opportunity to directly feel the pain that results from a healthy person trying to carry an unhealthy person and treat them as an equal. Invariably, the unhealthy person has the most power and decision making ability, while retaining the least responsibility. The unhealthy person also tends to be the one that the couple's children treat with the most respect and consideration because they have been taught by both parents that that one is the most important. You may invest 40 years before coming to this conclusion that you can't make a relationship work by yourself, you may even stick with the relationship at that point (but without hope), or you may decide to cut your losses.
In the process, the healthier person usually becomes quite isolated or else has to develop a separate life apart from their partner even if they are still together. Often in the end, it is the unhealthy person themself who leaves, leaving the person who has borne the main load feeling bewildered, hurt, angry and embarrassed. I see a number of people close to me in various stages of this process and I'd implore you not to do the same.
It is not that the other person is a bad human being, but rather that they just don't have the resources it takes to build a lasting relationship (at least at this time). Before you undertake any major building project or cooking venture, you would evaluate whether you have the right ingredients and if it is realistic to be able to get them if you don't have. This, while more serious, is no different...