When I was reading your post I kind of feel like you answered your own question in there without even knowing it. You MUST be special to your T for her to stick with you. She sees things in you you probably don't see in yourself. And she is working really hard to help you. You don't try so hard for someone you don't care about. She'd just let you push her away and forget it/you. If you were just a way of paying the mortgage don't you think she'd find someone "easier" to pay it!!!!! Even if you were a "challenge" for her, there's no way she'd stick it out if she didn't think you were worth it.
There's all different ways of being special. It definitely sounds like you are...
Have you talked to your T about finding it hard to trust her?
LTF