Hi everyone. Thank you for your thoughtful replies.
WePow, good point. This is a big one for me because I am very good at making sure everyone else is happy. Sometimes it does feel better to push myself and go out if I'm on the fence. But this wasn't like that. I felt like all of the life force had been sucked out of me and I just needed time on the couch to rest. I told my partner I might be able to go if I had a super extra large cup of coffee. But I knew this wasn't the healthiest idea. It was the only way I would have been able to pull a semblance of myself together and the main reason I would be doing it would be for her. It felt like better self-care to go into rest mode.
I still felt guilty because my partner said she was disappointed (though she said she understood). Then when T said what she did I felt like... sometimes what looks like withdrawing (depression) is actually just tending to one's own needs, you know?