I think you miscategorized the reason for your going back to the first guy. It is not that he was familiar. It is that you felt challenged by his seeing someone else, and, as you aptly said, "FOUGHT to get him back". Now the question is - was the fight worth it?

So you are not sabotaging yourself and no, you do not love being miserable - you simply love winning more than you love being happy. You removed the new woman from the familiar man's life (at least for now) - that was your win. It made you content for awhile, but not for too long. If you look at it calmly and consider how much you are paying for the victory, you just might realize that your personal happiness is worth more to you than making that other woman lose. Think along those lines - just very calmly, without any guilt - and see what makes most sense for you.