Don't get confused by the title. When you are finding the right man for you, there isn't only one rule. However there is a rule that I see important enough to write a whole post about.
Rule: If you find yourself justifying his wrong actions to your friends or family instead of letting him take responsibility then don't go further.
Whether or not he will make an excuse for his behaviour is one thing. But when you start making excuses for him is when it gets dangerous. I am not a love coach or a therapist or anything of the sort. But instead I say this because I was in a toxic relationship where I defended everything he did and completely lost myself to it. When he dumped me it was because I had no self respect and I wasn't helping him grow, I was doing the exact opposite. What someone thinks they want is not always what they need or what is best for them.
The thing is the more we speak things out loud the more we believe them. It is possible to do this so much we actually forget what is true. Truth really can set you free. Not everything your boyfriend does is the business of your family or friends. But when things become public they should be addressed publicly.
The best way to maintain your dignity in these cases is to let him take the fall. Be kind about it but truthful. "Yes, he did a bad thing. And he will show me he is a good man regardless of that action". This sentence shows maturity and will prove to your friends and family that you are mature and ready to be with this man. Because believe me, it will break you down to justify it. And if you're continually justifying him to make it seem your relationship is solid. It will only make him think that his actions are acceptable. In the long run this will burn it down.
It's important to be okay with being alone a while. Because you don't want to have that pressure of finding someone, or you will lower your values.
So when searching for a great man, check yourself and make sure you're not setting yourself up for failure. And if a man isn't able to take responsibility it's time to think about the future of your relationship.