Gigolo

Turns out lover boy resents being called lover boy. He said "in my language that sounds like gigolo". So I agreed to stop calling him that. To his face :)

According to Cambridge:
lover
noun [C]
1 the person with whom you are having a sexual relationship, but are not married to:
They were friends before they became lovers.
She had a string of lovers before her marriage finally broke up.

gigolo
noun [C] plural gigolos OLD-FASHIONED
a man who is paid by a woman to be her lover and companion.