I have a friend like this,
She has a boyfriend, insists me and her are just friends, is rather adamant about that.
But recently changed the privacy on 2 of her Facebook posts where she spent 2 separate days with me “as friends” because she was probably worried about her boyfriend seeing them.
I can say to you that in same way she is emotionally cheating on her partner, yours is also.
Last Thursday she even came to my house insisting I looked at something for her, which her boyfriend did and messed up despite her insistence he did it correctly… rather than ask him to look again insisted to come to my house.
After tried to say that not seeing me in 6-7 weeks was ages and put a laughing emoji with no comment when I joked it was an excuse to see me.
So yes your partner is emotionally cheating.