AITAH for saying thank you to an employee who was flirting?

I (f23) have been dating my bf (m23) for 4 months. For context, I’m autistic and have ADHD and he has known that since we started dating.

Tn we went to the grocery store to get food for dinner, and I always insist we split the cost, so I was paying for my stuff at one self-checkout machine while my bf was scanning his at the other. My card didn’t go through, and some employee came up from behind me to ask what happened. I just said “my card didn’t work but it’s ok i’ll just use this one, thank you”. Didn’t look at him, didn’t smile at him, wasn’t paying attention to anything except my groceries. My bf asked what happened and I explained. We then got our stuff, and on the way out, the employee said have a good night. Again, without looking or smiling, I said “thanks”.

My bf was quiet on the way home. I asked if he was okay and he said “yeah, do I not seem okay?”. Then it was silent some more because he wouldn’t respond to anything I was saying.

We parked the car and he asked if he had to point out the obvious. I asked “is it that I said thanks to the employee?”. He told me that the employee was clearly flirting with me and my response was unintentionally inviting it. Apparently the employee was getting weirdly close to me and was smiling over at my bf multiple times while talking to me. I explained that I had no idea, and on the way out I said “thanks” in a monotone voice because I wasn’t paying attention to anyone around me other than my bf.

He said that any time a girl flirts with him in front of us, which does happen frequently, he doesn’t look at them, he doesn’t respond. Maybe he’ll nod or shake his head once if they’re asking a yes or no question. He doesn’t entertain other women, and he told me that my “thank you” didn’t sound monotone. He doesn’t think I was flirting back, but he said that this is the second time I’ve straight up missed the very obvious social cue of men flirting with me.

He got upset and said he was driving me home. What’s worse is that we nearly broke up rather recently due to me missing social cues and him interpreting it as me belittling or not caring about him. He finally believed me in the end that while my actions weren’t okay, it was a matter of poor judgement on situations rather than me using him and being unloyal. He said he understands I can’t get every social cue, and it was his responsibility to not take it to heart when it happens anymore. I said I would try to be as observant as possible and would do all I can to think before I talked, but yeah, at the end of the day I will still miss certain cues no matter how hard I try. Then today happened. He said I ruined the night.

The first time something like this happened, it was also with an employee. So I trained myself to simply not thank, smile at, or respond to them (which is admittedly difficult bc I’ve worked retail for 5 years and understand how rude customers can be and I feel a little bad for ignoring other employees now as a customer). When I told this to my bf, he told me it’s not about going from one extreme to another, but finding a middle ground. You don’t have to be an ass to employees, just know time and place. So that’s what I tried to do today. Still thank them, but be very aware of my body language, don’t be overly talkative, just respond when spoken to. And then I of course miss the flirting social cue completely. Maybe that’s why I went from being kind to workers to fully ignoring their presence when I’m around them, because I’m scared if I do say anything back, I’ll miss an obvious social cue.

Am I the asshole?