My wife and I are still best friends 15 years after we first hung out. I'm pretty fortunate that we rarely ever get into it. Maybe once a year we have a "fight," but it's not a "GET YOUR SHIT OUT OF HERE" sort of ordeal. It's good to vent once in a while, so have at it. If the other person in the relationship can't accept some constructive criticism, then they honestly need to **** off.
I made mistakes in previous relationships, looking for things that were never there. Discovered how to spot crazy people helped, but found out that crazy can evolve in a relationship. The old adage of "study her mother" is key. If her mom is cool, chances are that she'll be cool. If her mom is a nutbag, some of those genes were passed on. Of course this isn't true 100% of the time, but my crazy ex had a batshit crazy mother, so there's some truth in there.
I also found that the best fucks tend to be the craziest fucks, so next time you think of ass to mouth with your lady, you better make sure she doesn't lop off your nuts as you blow your load in her face.
Know how to roll the dice.