I ended my relationship with my girlfriend about 3/4 months ago cos i needed some space...

Split not even a month and she's sleeping with another guy? Agreed to get back with and marry you while at the same time still sleeping with this guy? Cold and distant? Shows no remorse? HELLO!! ANYBODY HOME IN THERE?!! How many more red flags would you like displayed to show what your future is going to be with this woman?

I'm quite sure your heart is telling you something here ... probably waving red flags left and right trying to get your attention. Do you feel that knot in your stomach that feels like something is not right? That's it. You've answered a lot of your own questions here. You say you hurt her ... perhaps you did ... BUT if she said she was going to give you a second chance, why is she not? You said "she loves me and wants to be with me, but she's still really cold and distant, and doesn't show much remorse for what she's done" and "she had still been seeing the guy behind my back til I found out a few weeks after our engagement." Not going by her words, but by her actions, is that what you consider love? Either she is resentful of the past and not likely to get over it or she is outright lying to you. Resentment is a hard thing to live with, and you will even start to feel it eventually. Perhaps the reason you needed some space to begin with was because you sensed something not quite right, but while you were apart, you began to think on the good times and ignore your heart's message. I've seen things like this happen too often. Even lived my own version of it. It doesn't get better, it gets worse. I know this isn't what you want to hear, so I'll ask you more questions. If you knew or even thought this is how it would be for the rest of your life, would you chose it? Would you possibly want to bring children into this situation and be further trapped? If (when) you found someone who loved you AND showed it, would you want to be free to be with her? Listen to your heart. It actually spoke quite a bit in your posting ... "but she agreed to get back with me and agreed to marry me, while all at the same time still sleeping with this guy" says it all. There is nothing lonelier than being with the wrong person. Don't worry about what people will think if you break off the engagement. It's easier than a divorce.

Work through it....perhaps....but now you need to give her the time to decide what is best for her, as she gave time to you. You may well have to give her up, but that needs to be her decision and one not motivated by pressure from you one way or the other. You messed up this time, bud, learn your lesson.