Sometimes it does get hard without a bit of outside help. Especially if one of the persons has a PD. And thats not any different then one of the persons coming down with a terminally disease.
I beg to differ, having experienced marrying, loving, and living with my husband who came down with a "terminal" disease.
You are not married. You get what you get when that little piece of paper means so little. Considering the cost of a divorce in deciding whether to marry is a pretty good indicator that you are both renters. You're right though, it is a choice you both make together but you're wrong about whether marriage makes a difference in a relationship. Terribly wrong.
As far as getting outside help, there are plenty of relationship counselors. Nothing hard about that. The hard part is making the choice to stay in a relationship that lacks the commitment of until death do us part.