Emopunk, let me give this a try.
You made a few mistakes here but I don't think you are a lost hope for future relationships.
I myself do not trust women as far as I can throw them. As much as everyone tells me to and to give them a chance, I cannot. There are no certanties in life.. and a relationship is definitely not one of them. There are many conscious and unconscious factors at play when it comes to love and relationships regarding the way a woman will perceive you. More often than not, a lot of men do not realize this is even happening, if they are getting lucky or failing miserably.
Don't play their games back at them, they will get even more mad at you than you did at them, and will probably end up leaving you if it persists. I don't really think that it was your fault for that, because she was lying to you. You definitely have to be a man and call her out on her BS from time to time too. You can't always say "oh its ok baby" because she will think you are a pushover. You are a man who demands respect, and gives it in return. Remember that.
I don't think anything myself or anything else here will convince you to be more trusting of a woman when she goes out with her friends, or to a bar or club. I won't sugar coat it, men are probably checking her out or trying to get with her. That's the sad reality. They don't care if she is single or if she has something with you. Nobody these days respects the boundaries of a relationship. It makes me sick, but that's just the way it is.
I definitely feel where you are coming from not wanting her to leave your side because there's always that risk of another man stealing here away. That's something you have to realize and understand, it's a risk you take when you get into a relationship with somoene. For the future, you need to be prudent and picky in who you select as your partner. Make sure it won't be someone who does this . I don't care how pretty she might be, don't settle for her if she isn't someone you can TRUST and who can be MATURE and HONEST with you. No amount of good looks can compensate for a lack of those qualities in a woman. I'd date someone less good looking to have those qualities.
Bottom line: Even if you can't trust them or aren't confident in yourself or in her. Do not show it. At least create the illusion that you are the most confident, trusting guy there is. Worry about her all you want when she is gone, but don't confide in her that you are worried or that she can't be with other men. After she hears this from you over and over again, she will lose her attraction for you because you are too naggy and aren't confident enough. At least fake it if you can't be trusting.
Hope this helps for the future