For the pursuit of marriage, it is imperative that we never make the mistake of thinking that we are dating a saint, and we are too sinful, weak, or broken for that person. It is also imperative that we do not put that other person on too high of a pedestal, and remember that they, too, are a sinner. If you are ever dating someone who comes across as believing there is nothing wrong with them, and they are picky and critical of you, please run away from that person as fast as you can and never look back.
To have an awareness of your own shortcomings is a great gift, both individually and socially. Individually, this gift helps you understand that before God, you are not yet a saint and have work to do. This should inspire you to keep doing the work of perfecting yourself by God’s grace. Socially, this gift helps you to approach other people with true humility, knowing that you are not "better" than anyone else. You feel honored when someone is interested in bringing you closer into their world. It also helps you approach this person in charity, knowing they have their flaws and issues, and these should be things you accept and gently help the other with.
It is a mistake to be turned off by someone's negative qualities. It is much better to be inclined to seek the good qualities. Let those good qualities overshadow any negative qualities, and (hardest of all) attempt to accept and even embrace the negative qualities. This is the secret of finding a suitable partner for marriage and being willing to make the commitment to that person. Once you are able to find the negative qualities endearing, and understand how both your qualities make you unique as a couple, then you are have what it takes to make marriage last.
If it sounds like what I am saying is that falling in love involves loving the negative as well as the positive, you are correct. Love is a total acceptance of the person, flaws and all. Deep love is experienced as the negative qualities take on an endearment to you. A marriage is in trouble when the two only love each other as their good qualities are experienced. The negative qualities have to be embraced and loved if you are to love each other for a lifetime.
Marriage is where two sinners come together in the lifetime commitment of being each other's path to sanctity. They have good times and bad times. The good times make life easy. The bad times make life challenging, perhaps even a hell on earth. The bad times are often moments where one is experiencing negative things from the other. It is in those moments that our character is tested and our opportunity to take a step forward toward becoming a saint is given as a gift from God.
The security of the sacramental bond protects the two sinners from losing their primary opportunity to become a saint. The union allows the two to fall without the fear of hurting themselves beyond repair. When one falls, the other is there to help navigate them back through the love accomplished by patient endurance, kindness, silence without reproach, and forgiveness. Perhaps it will take being the one to say "I'm sorry" when it is the one who has fallen who, in justice, should be the one apologizing. That is the mercy that true love brings to marriage and mirrors the love of God.