One of the biggest mistakes I have made in my life and I have seen in other men's behaviour is seeking validation. This is not limited to looking for it from girls but also from other men. It is proof that you have no confidence in your paradigm of the world.
Asking others' to confirm your opinions or views about the world is essentially saying, "Hey I have no confidence in anything I have learnt or seen in life, please tell me how you see the world and I will copy that". Lot's of young fall into this trap. And considering how fucking nonsensical the world is, it's understandable. But you are going to get nowhere in life if you keep looking for others to confirm your views on the world.
There is a distinction between accepting what you don't know about the world and looking to learn, and not believing in yourself. The first is a display that you don't know everything and that you are looking to expand your view on the world. The second shows that you can't even trust yourself. It is unattractive to men and women.
If you think someone has fucked you over, believe it. If you think a girl is messing with your head, believe it. If you don't trust your old friend, believe it. The more you believe in yourself, the more confident you will get in your own choices because you will start making the right decisions and gain a confidence you never had before.