My wife returned, but

I've brought something infuriating again

This time, I didn't write down what to call Brian...

Mistress/Lover - Feels too much like a modern melodrama
Boyfriend/Girlfriend - The atmosphere seems light
Lover - The word feels affectionate for an affair
Concubine - It feels like Joseon Dynasty Korea, not a Western fantasy romance

I'm asking you, users, what should I call these guys?

It's too late, I should have added this sooner, but I'm adding the summer picnic image now!!