Eeeeh, not many focus on that and my memory's rusty...
In Dreams of Desire, you can get your bro hooked up or ntr him and then get ntr'd by him. - iirc.
In Superpowered, one of your sidekicks gots the hots for PC's mom and you can get them going, if you want to.
In Summertime Saga, you can get your boy a gf, or take her for yourself.
I think in ICSTOR's Milf's Villa, you can help the frend you're staying with, but i'm not sure...
Same ICSTOR's Milf's Control lets you mind control the teacher for some reluctant good time with your card buddy.
In Treasure Hunter Mai, by Gyu, everybody can get fucked by everybody. (female protag and team - there are a few several games like that)
In Goons Raid Her, you help everyone else screw a Lara Croft wannabe.
In Porn Empire, you have a porn company where you decide the actors and scenes.
In Lilith's Throne, you can have a companion that gets screwed in stead of you in a defeat scene.
In Eratohok, you can have your subordinates screw each other or get screwed by others.
In Girl Life (fem protag) you can have PC's brother fk a classmate owing you money.
In Life Play, all toons can have a relationship with each other.
May be others, but i can't recall now.