My Wife Is Back

I've brought something that will make you angry again.

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

Mistress/Lover - Feels too much like a modern melodrama
Boyfriend/Girlfriend - Seems too lighthearted
Lover - The word seems too affectionate for an affair
Concubine - Feels like it belongs to the Joseon Dynasty of Korea, not a Western-style romance fantasy.

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

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