How do i stop forgetting important things?

Long story short, i forgot to attend something important with my girlfriend of 3 years and it isn’t the first time i forgot something important.

Those were events that I cared about and wanted to attend / remember but for some reason my mind just blanks out on those days and i completely miss the mark. It’s not even relationship things, general things like meetings or submissions are things i forget about as well.

I do have generalised anxiety disorder, but I don’t want this to be a cop out for me to forget anything when things get stressful around me, which causes me to hyper fixate on the task / event causing the anxiety.

Any suggestions to deal with this? I’ve tried joint calendars but they don’t really work for me when it comes to remembering; I currently just try to remember what is being told to me.

I understand what I’m doing (or not doing in this case) is very bad and I just need some advice to improve on it.