Summarize:

It turns out that trust is a lot like everyone’s favorite nursery rhyme egg, Humpty Dumpty:  it’s easy to break, and very hard to rebuild afterward. Once you’ve betrayed a girl’s trust, “all the king’s horses and all the king’s men” may not be enough to get it back.  Sometimes you’ll just have to accept that it is lost forever.  But that doesn’t mean you shouldn’t try your hardest to earn it back. Never assume that you deserve a second chance, especially if you have seriously betrayed her trust, such as by cheating on her.  Earning trust is hard, and re-earning it is that much more difficult.  Don’t fool yourself about the substantial effort it will take on your part, and the reality that it may not be enough not matter what you do. The first step to regaining trust is always to be completely honest (to her and to yourself) about what you did to lose it in the first place.  Think long and hard about why you did the thing that broke her trust, and be prepared to patiently answer her questions and accept her anger and sadness. Never try to downplay what you have done to break her trust.  It is serious business, and you need to always treat it as such if you want any shot at regaining her trust.  That said, once you’ve “come clean,” try not to obsess over why you did it or the “gory details.”  At some point, both of you have to be able to move forward if trust is to be rebuilt.  You can’t control her pace in moving past it, but you can control yours. Never make excuses for your indiscretions that have caused a loss of trust.  You screwed up, it was your fault and yours alone, and now it is up to you to do everything you can to rebuild what your actions have broken.  As with coming clean with all the details, a full apology is necessary to “clean the slate” before you can begin working to restore trust. Saying “Sorry I messed up.  I promise I won’t do it again” will not cut it.  Try something more like:  “I am very sorry that I lied to you about something so important.  I know how much it has hurt you, and it is all my fault.  I hope you will give the the chance to earn your forgiveness and regain your trust, even if I don’t deserve it right now.” Sometimes people can become so focused on admitting their errors and begging for forgiveness that they never get around to forgiving themselves.  We all make stupid mistakes, and hurt people we care about.  Without minimizing the seriousness of what you’ve done, you need to be able to accept it and leave it behind if you hope to move forward.  If you can’t get past it, she’ll definitely never be able to.  Regaining trust is hard work, and requires you to make real changes in your life.  If you’re too busy still punishing yourself for screwing up, you won’t be able to put the work in that is necessary to regain her trust. Remember, you can’t take back what you’ve done.  All you can do is try to make amends for it and prove that you’ve learned from this mistake and won’t repeat it. Earning forgiveness and regaining trust take time, and they have to happen at the pace set by the person who has been harmed.  Your actions and words will help determine if the process succeeds, but you can’t force things along.  Sometimes, all you can do is wait and hope. Expect setbacks in the process.  Things may seem like they are going well, and then all of a sudden she can’t stand to look at you again.  The truth is that the sting of a betrayal is never going to completely vanish, and like any old injury, you have to accept that the pain is going to “flare up” every so often, and sometimes for no apparent reason. You broke her trust, and you have to do much of the heavy lifting in order to stand a chance of getting it back.  However, she has to be willing to put in the effort as well.  Only by working together can trust be restored.  If she can’t or won’t join you in making the effort to rebuild things, take that as a sign that the break is irreparable. If open and honest communication is important to building trust, it is even more vital to rebuilding it.  Be willing to talk and listen a lot.  Don’t hold back, and encourage her to do the same.  Consider engaging the help of a therapist or counselor trained in dealing with broken relationships.  If she raises the idea, never hesitate to agree.  If it’s your idea, give her the time and space to consider it.
Don’t take it for granted. Come clean but don’t obsess over the details. Apologize unconditionally. Forgive yourself. Be patient and understanding. Work together.