Disclaimer: I know nothing about this relationships - but here's my theory. I've noticed that everyone has that one fatal flaw in life that affects every relationship that they have or pursue. I've been able to identify a fatal flaw for most of my closest friends and they seem to agree, but also defend it.
I'm not saying that people only have that one flaw - it's more that there's one flaw that outweighs the rest. Think about watching basically any rom-com movie where they highlight that one fatal flaw the whole movie. The women who can't get over her ex to date the new guy. The man who works too much so he pushes the girl he loves away.
For example, the friend who's too picky. She never gives anyone a chance. Her defense is that she doesn't want to date just any guy. Having high standards is great, but I would say it has translated to a flaw that has prevented anything from happening.
Or, the friend who makes excuses for her boyfriend because she's blinded by her love.
Anyways, if you think really hard you can probably identify what your fatal flaw can be. It's unlikely that you can correct this flaw completely, but it's important to be aware of it. The fatal flaw is not only identified in romantic relationships but often platonic too. You may be overly defensive of your boyfriend/girlfriend and also of your friends. It's just a part of your personality at this point and you should try your best to make it a strength rather than a weakness.