Struggling with Self-Harm in a Healthy Relationship

TW: SH I SHed for the first time in 4 years yesterday. I’m in a healthy relationship (been together over two years) and I don’t know how to tell my girlfriend without making her feel guilty. It happened after a fight we had, but I had already not been okay. She had made plans even tho we had plans and I was using those plans to be okay. I would’ve been okay if we didn’t have plans but the fact that we had plans led me to rely on her being there just to decompress. I tried to be vulnerable, which is really hard for me, and the consequences of letting myself fully feel my emotions are dangerous but I thought I was able to let myself and not be alone. I would not have really even gotten upset if she hadn’t disregarded our plans because I was doing what I needed to emotionally but she was a part of that process. I talked to her about it and she feels really bad about doing that because it’s also something I’ve mentioned before, that canceling plans can be really hard on me. It was honestly the fact that she didn’t ask, if she had asked if it was okay if she did x instead than I would’ve said yes and been okay. I really was not okay before and then relying on her being there and her not being there and then she got defensive (which she struggled with) and unintentionally gaslit me (which she has NEVER done) and it was all a lot and triggering but it was mostly because I wasn’t okay before. I wouldn’t have been that fragile if I wasn’t relying on our plans or if I had at least had a choice in the matter. I haven’t told her I SHed and it obviously was not her fault. My reactions to my emotions are not her fault but she might feel like that. I also just don’t even know how to explain why I did it.