I confess, I didn't even read this thead. Relationships are not fixable because they are not static - it's not like changing the muffler in your car or repairing a broken window pane. Relationships change all the time because people change all the time. For me, in any relationship in my life, I wouldn't be thinking about "repairing" so much as "prolonging." So the question becomes, "Do I want to prolong this relationship or not?" Notice the question does not include an assumption that the relationship will change to my liking. It will change, no doubt (I've a bit of experience here since I'm mother of two, and I've been breathing for half a century now). I can't fix relationships - I know that. I can hang in there or not, depending on how important the other person is to me, depending on whether or not I see hope of change (assuming that longevity of the relationship is dependent upon something changing).
The whole thing about changing a "relationship" is that you are - at most - only 50% of the problem. See how I said that - problem-you, related? If there are other people involved, you are likely much less than 50%.
What I know: Strong relationships heal, just like scrapes and sunburns. Nothing in my mental abilities allows me to heal scrapes and sunburns, but I can try to aid their healing. An emotional Band-aid is the best I can do for relationships. If that isn't good enough - everything I can do is just not good enough. And that's the way it is because the person who I'm trying to have a relationship with has his/her own minds, their own beliefs and their own ideas. I so love that in a person! So I love that person, but what if that person doesn't love me? Maybe later, maybe not - I can't change such a person. I wouldn't invest energy into a person who would be very changed by me. What would be the point?