When we feed off each others anger

We have been dating for over 4yrs I have come to notice she is the type of person who in an effort to shoe independence she won't be very open about her problems, instead she keeps them in and eventually develops a short fuse. Lately money has become the underlying issue and me constantly finding myself in my own obstacles ( transportation issues, work, finances..) in am effort to not add to her plate I try to deal with them on ny own, but another of times they end up getting in the way of us, causing me to be late or not be able to come through for her financially. She also has a 7yr old who's father is never there in any way shape or form. As of lately it feels as though she wears out her patience with everyone else except me and results in her getting upset with me easily.

Now when she gets upset she can be very cold. I never intend on upsetting her, but she hates that I apparently have an excuse for everything, which to me is not an excuse it's simply what it is. But she gets very bothered by that to the point where she says she has had enough and tries to end it. I on the other hand am very persistent. I love her more than she will ever know. And I find myself fighting for the relationship because I empathize and I do take responsibility for contributions to her stress and I try not to add to which has resulted in me lying to avoid making her feel like I'm another problem however she has caught me lying which has led to a trust issue. The thing is though she knows and has not doubts about my loyalty. My lie was regarding where I was so it wasn't about the lie itself but simply the fact that I did lie. And as I mentioned when she gets mad she gets cold and will do a hell of a good job making me feel like she doesn't care or is unphased or will be fine without me, and that kills me. But I try to see passed it and instead be the bigger person. But lately it's getting harder and harder and I feel like if the underlying issue doesn't get resolved then we may not make it.. because is harder for me to be the bigger person I find myself being cold back or pretending I don't care either which feels like just led to a distance between us to the point that when we are good we aren't as good as we used to be. So I don't know what to do or how to get back to before all this I don't want to lose her.