Lover
Mistress
noun
The person you make love to is your lover. Woooh! Don't worry I won't tell. Have fun and be safe, kids.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
お前は愛人にすらなれなかったんだよ。
You couldn’t even be his lover!
愛人っぽい顔してるねって言われて、すごくムカつきました。
I was told I looked like a mistress, which really pissed me off.
今日は愛人の家でご飯食べてくるから、晩ご飯はいらないよ。
I'm going to have dinner at my mistress's house today, so I don't need dinner.