I wanna keep this short, but I promise I won't exclude any information
So today is Ash wednesday in the Catholic faith, and I got my ashes done on my forehead. They're quite prominent, but it doesn't bother me. I live in quite a sectarian city that I won't name. Catholics and Protestants have had a long hatred of eachother which has only started to recently cool a bit. I'm not a catholic in the religious sense, probably more agnostic, but I come from a catholic family. I should note, where I live, being a catholic generally equates to a nationalist while being a protestant generally equates to being a unionist. I am a non practicing catholic bordering on agnostic and am 100% nationalist. My girlfriend is not religious and is 100% unionist. 

So after I got my ashes done we went out for the day. I didn't tell her I'd got them done so I thought it would be a bit of a shock, but not a big deal and we could laugh about it. When we met up, she immediatly told  me off for getting them, that I shouldn't have cause I'm not religious. She refused to walk next to me, and after saying I look like a retard she half-jokingly said that she didn't want to be seen with me and if she'd have known she'd have just went out with me tomorrow. she insisted I wash it off but I refused. While I might not be the most religious person, I am proud of where I come from, and I find that participating in religious events from my culture is a good way for me to express that. 

I told her if she was going to be like this then I'd simply get a bus home, she walked on past me. While I was waiting she texted me and essentially told me to come back, she was getting cold. When I got down to her, she was on the phone to her friend. Her friend was in the same place we were headed so she planned to meet up with her. This kinda hurt, it seemed like she wanted someone else to be around so she wasn't alone with me. Her friend is also protestant, and I didn't want to be made fun of by my SO and her friend. I made up a story about having a test to study for tomorrow so I had to go home. She gave me an annoyed "bye" and walked in the opposite direction. 

I don't see the problem, I like getting my ashes done, even it's not for explicitly religious reasons, it's just something I've always done. I don't agree with her political beliefs but I don't belittle her for it, I occasionally make light digs if it comes up in conversation and apologise if she thinks I went too far. 

This happened about an hour ago and we haven't spoke since, normally, we'll both apologise in an argument, but I don't feel i should this time, I feel I've been treated wrongly for simply getting a black cross on my forehead

So Reddit, I know nobody wants to get involved in religious debates, but AITA?