Toxic Relationships

So I've been doing a lot of thinking and 'soul searching' these past few months, and there have been some things that really bother me. I've definitely noticed a pattern with females... Why do we constantly surround ourselves with negative influences in our life? Life is too short to surround yourselves with people who just bring you down. Some people in our lives have done horrible, even unspeakable things to us, yet we just move on and keep them in our lives. I'm not saying that we need to just kick people out of our lives (although I've definitely been guilty of that before) but we definitely need to evaluate our relationships. Some people are able to forgive and forget but I'm not always one of those people. There have been people in my life who have hurt me pretty badly and I have let them back in but with my stipulations. I make sure to keep certain things personal in my life and only share what I choose to share. I suppose I'm guilty of the same things from time to time but I'm going to try and be more aware of it. I'd appreciate any comments you may have.