<human>: Can you condense the text into a few key points?

I have been with my fiance for 7 years and we're due to get married in March. I have lied about stupid and small things (like ordering a credit card, talking to someone etc) and been un-supportive and lazy.

I have been trying to improve myself and be better to her, but I keep failing. She has been amazing to me and tried to help me come up with action plans to fix things, which have helped a lot, but trust has already been broken and everything something happens it just reopens the old wounds I have caused.

Everything I've see have said this relationship is doomed, but I love her so much and have to try and fix it. She has talked about breaking up, but she also still loves me and wants to fix it, but she is unwilling to simply "give me another chance". I completely understand her point of view and take full responsibility for my actions, but it's come to the stage where things can go from being OK to us fighting because she doesn't trust me or that I'm even trying to do the right thing.
   
I need a way or plan or action or guarantee to present to her that will help me become the person she deserves and help her have enough confidence in me to give this another, final chance.
<bot>: Have lied, broken promises and been unsupportive multiple times. Partner is willing to work on it but wants a guarantee this time will be different. I'm lost and desperate to change and fix this.