Am I too insecure or is she really pushing me away?

Hello. I am a 27 year old man with some insecurity issues. When i was 21 i was engaged only to find my fiancee cheating on me. It took me many years to even consider dating again. When i was almost 26 i met this new girl that literally was something from a dream to me. She had everything I ever wanted in a female. (this is not the first girl i attempted to have a relationship with after my fiancee broke my heart) As the story goes, i broke a promise to her. Though i never cheated (and was never even close or in a situation that could be misconstrued as such), it made me feel terrible. I didn't intentionally keep it from her because I literally had forgotten. Ever since then it feels like things are just a little tense between us. This has been about a month. I tried talking to her about it once and she said she didn't know if she could trust me. I'm not sure if she is over reacting to the situation because she had been cheated on before, or if it really was such a big deal that i forgot to tell her when a particular girl talked to me. In any case, it seems our relationships have ups and downs. I find myself constantly at a loss for anything to talk about with her. I'm not afraid to say something wrong, i just don't know what to say. she doesn't seem quite as bubbly around me as she used to. Sometimes i wonder if she doesn't consider this just a relationship of convenience. That i was just lucky to be in the right place at the right time and our little fight made her realize this. Should i talk to her about this more? I just don't know... I have always tried to be there for her when she needs me. She has a lot going on in her life. She was diagnosed with a pineal cyst and it's causing issues with her balance and in turn is creating severe anxiety for her. I wouldn't dream of leaving her when she needs someone to be with her through this. I'm not saying that her need of someone to support her is my reason for staying but I guess i'm just trying to say that despite those health ailments I still want to be with her. I can honestly say i love this girl and am willing to change my own life and happily inconvenience myself to make sure she's happy and taken care of. I'm sorry that this is so convoluted, i'm trying my best to let my my feelings write this so i don't miss anything. I guess what i really want to know is; Should I talk to more about how i feel since that day? should i just let time help cool her down? Am I just too insecure and being way too over-analytical?? Any perspective is welcome.

You really need to state what promise it was you broke to her. And besides that you need to understand that this promise obviously meant a great deal to her. So even if you see it as "no big deal" she may think otherwise. If it was so important that you had to make a promise over it then its a shame that you didn't remember to keep it. See its not always about what you think is important, its about what the other person thinks is important and if you are willing to respect that. So you made a promise, you broke it. Now she feels betrayed. You may want to talk to her further and understand that her trust in you has been damaged and don't make promises you will not keep. Its not always about cheating, its about trusting the word and promises of your partner.