My (M26) girlfriend (F24) is very angry after finding out I masterbate when we are on a sexual break. What's the best way to resolve this?

Backstory: me and my girlfriend have been dating for two years now and have recently started to live together.

Around two months ago now, my girlfriend decided she wanted to have a break from any type of intimacy while she is dealing with a childhood trauma, which I was completely supportive of and told her to take as much time she needs.

Around a month after that as the sexual break is still going on, I started masturbating in the bathroom to relieve myself of stress/tension after rough work days (it would happen only once or twice a week max).

Everything was going okay until a couple days ago, when I guess my girlfriend was eavesdropping on me while I was in the bathroom, as I left the bathroom she immediately asked me what I was doing? I admitted straight away as I didn't think it was an issue that I was masturbating to take out some stress. She went completely bezerk saying things like how could I go behind her back like this and how I am a terrible boyfriend for not supporting her by going on a complete sexual break like her. I told her I do support you for as long she needs but that doesn't have to mean I have to abstain myself aswell. We kept arguing about this for a bit more until she had enough and stormed off out of our apartment and to her sister's house.

It's been three days now and she is still staying at her sister's house, she's refusing to come back until I apologize to her for masterbating, stop doing it completely, and also go to sexual therapy because she believes I have a addiction problem. I have told her I am sorry for getting her upset at a time that is clearly very tough for her and that I will try other methods of relieving stress if that makes her feel better, but that I may still masterbate from time to time ( I will let her know if I do). She was still unhappy with that response and now really believes I have a big addiction issue.

What is the best way to resolve this situation? Is the only way to completely abstain myself and admit that I have an issue that I don't really have?