My partner and I just had a talk about it. Basically, she celebrated her birthday today. I was on her party, and it was fun, but I left after around 2 hours to get home and relax a bit. After I arrived, a friend of mine texted me and asked me if I wanted to go to a lake and see the sunset. I agreed, we went to the lake and went swimming in it; it was really nice. Later, after arriving at my partners, she talked with me that it hurts her that I went out with someone else on her birthday, doing a romantically coded activity.
To be honest, I realize that I don't have a single clue what is coded as a romantically coded activity. For me, this was something completely okay and appropriate, because it is for me clearly a friend-thing; but my partner explained to me that the combination of going out with another person on her birthday and going to a sea, which is a secluded place, just heavily connotates it in a romantic way.
I understand that what I've done here wasn't right, and that I have responsibility here. Even though I didn't want to hurt my partner, it is still my responsibility to inform myself here on romantically conmotated things you shouldn't do in a partnership. So, dear people of Lemmy, what does constitute a romantic moment?
Edit: I've left out some information which seems to be important for the whole picture . I've copied it out of my comment and adding it here:
Me and my gf got together in August of last year, so basically 8 months ago; we were friends for half a year before that. She got cheated on in her long distance relationship before.
The friend who invited me to the sea I actually know for almost as long as my partner, from the beginning of Uni. She had a breakup from a three-year old relationship a few months ago, and I was there to support her. I didn't clarify before though if she was okay with me cuddling with people or not; I assumed it was with her, because it was okay in her LDR before - which was wrong of me. I overstepped the boundaries of my partner here.
The friend in question kissed me at the neck while I was at hers. I talked with her about it and let her know that I wasn't okay with it, to which she reacted quite hurt. She then told me that we shouldn't be friends, but two weeks ago she collapsed at Uni and I brought her home. Now we are meeting again.
While I'm writing this down, I'm actually starting to notice that there are a lot of other factors playing in why my partner is upset here. She has been cheated on in the past, which definitely leads her to feel uncomfortable about my actions, even though I obviously don't want to cheat. I broke a societally unwritten rule of not meeting people in romantically coded settings on your partners birthday. And I overstepped the boundary of my partner before by cuddling with the friend without my partners consent.
So I accidentally stumbled in here and I'm making some broad and very possibly weong assumptions that most everyone else in this story is allistic. If that isn't true you can probably ignore this, my bad.
That said OP if your GF is allistic, and especially if this is a newer relationship, you may need to tell her that she needs to clarify her expectations explicitly with you in this area. If she is allistic there is no chance she'll have thought she had to ask you "please don't abandon me on my birthday to go on a classic date with someone other than me." To an allistic bystander this whole story reads like you care more about this friend than your girlfriend who you dont seem to really like all that much. (Not saying it's true just that that is gonna be the social impression given off). Also, if you didn't do something romantic still leaving your partners party to go hang out with a friend will still largely be interpreted as prioritizing that friend over your girlfriend. I'm not sure if that's what you were trying to do but that's what allistic people who hear this story will assume. So if she was OK with you leaving the party to hang out with this friend nonromantically (which seems unlikely) you may want to include "my GF told me she was fine with me leaving her party" when telling this story. Otherwise I think you focusing in on just the romance part may be missing the point, the romance part just made it worse but wasn't the whole problem.
Also as a side note: if the friend who asked is of a gender you are interested in and knew it was your girlfriends birthday when extending this invite (and is allistic) then your friend was knowingly being an asshole to your girlfriend. Possibly also trying to sabotage your relationship. Just a heads up.
Hmm, got it. Well, actually I left the party and then my friend called me; it wasn't planned for me to go meet her until I already arrived home.
When I talked about this with my gf, she urged me to put in some research in myself - which I hereby do :) I understand that she doesn't have to explain everything to me. But it also really hurts me when she told me that her two closest friends advised to break up with me if something like that happens again. So it definitely is societally frowned upon.
And thank you for the heads-up. The friend in question gave me a neck kiss, which I talked about and told her it wasn't okay. She is now in a relationship, and I really have the feeling she pays more attention to my boundaries now. But I'll keep in mind to stay vigilant. I don't think she knew my partner had her birthday today, but thank you for the warning regardless - I'll keep it in mind.