I was in the same boat as you, I treated my girlfriend more like crap than you and only made it 8 months. I did the whole begging thing, pleading thing dragged out over a whole month and a half and all the while she was talking to some other guy. I heard it from some friends that she was but I felt so guilty about treating her like crap, I wanted to trust her and give her the benefit of the doubt. Finally she told me about said guy, how happy she was, how over me she was and that was it. Everything just flashed before my eyes. At least you are not in that position but I tell you to be prepared. In such an emotional state as you are in right now, you are very prone to make a illogical decision (like you were with giving her the third degree tonight about where she is going and who she is with). That's why it's better not to do anything at all, rather than goof up anymore. If she finds somebody, she finds somebody. If she wants to be with somebody else, she will be with somebody else. All you can do is leave her be and not make her feel pressured, or in a manner of speaking, increase your odds of reconciliation.
You are certainly right though. I'm glad I wasn't taken back either because I wouldn't have learned anything if I didn't have to face the harsh reality and accept my responsibilities. I blew it too, and sometimes you only get one chance. It's a tough pill to swallow.
What you guys are doing right now is kind of dangerous territory. You want to be in her life so she doesn't move on or lose her feelings for you, and she is enjoying the option of talking to you and having that person to fall back on while she is going out and having a good time. And she feels justified in doing so. I just don't want you to feel like you are getting strung along. Everything is so uncertain and it could go either way right now. Just keep your head on your shoulders and your wits about you and like I said, all you can do is let her make the steps back towards you. She's going to be tenative because the break up's still fresh and there's a long way for her to go to get back to where you guys were and it's up to her to decide if that's worth it.
I've noticed that reconciliation usually happens after a good amount of time has passed, and it usually involves dating other people inbetween. When you are apart for a while, and then run into each other or reconnect again, it's like you are really getting to know them again and finding out things about them that are new and exciting. You know that spark, the reason why you guys fell in love with each other in the first place. It'd be kind of insane to think that things could ever be the same again between you two, but they can be stronger. That's why begging is so bad: trying to lure them back into a broken relationship, and reestablish it on such a shaky foundation: guilt, fear of being alone, etc. It didn't start out that way the first time, why would things be different trying to desperately get back together. You usually want to start a new relationship instead and that takes some time, some forgiveness and putting things behind you.
Just something to think about. Maybe it's not an option now but if things start to get ugly again, I'd recommend it immediately. Letting go is scary but could be necessary in the long run. And I'm sure you wouldn't care if she was with other guys if you had her in the end for the rest of your life right? That's what love is to me.
Waking up next to a beautiful girl,
Step outside and say hello to my beautiful world.