You've already attempted to let her know how you feel. If the break up too place recently, she may need some time to gather her thoughts. It is possible that she does not want to react while she is still upset. She could be fearing that if the two of you reunite, she may get hurt again if things do not work out.
Six years is a long time to just put behind. If you keep in touch with her family, you may want to try and talk to them. See what their perception is of what may be going on. If you were the one to initiate the break up, she may be angry. Anger takes longer to manage then disappointment.
If you are to write to her again (not texting or email) you may want to hand write her a letter, ask her at least to tell you when would she be ready to talk to you. Let her know that you are willing to give her the time needed to sort her emotions. Also ask if there are things she can propose to address this situation such as couple's counseling, pin point what had caused the break up and if that can be corrected.
She could be having a good time. That does not mean that when she's in the privacy of her home she's not upset or does not miss you. You've spent a lot of time together.
As far as her ability to trust you, that is something you have to work on. While she is not talking to you, try to figure out what makes you break your promises to her. She will want to see results not just hear words on your part. If you end up writing to her, you can outline your plan for how you are going to work on yourself while respecting her wish for no contact for the time being. You're having difficultly with impatience and that makes it hard to not pursue her. But, at the same time, that shows her that you're not able to do what you've promisesed her. She has to be able to trust you. That is very important in any relationship.