Neighbourly Love

My neighbours Joe and Ben are gay. They've been together for three years and Ben is the bottom in their relationship.
Even so for the past five months I've been fucking Joe during the daytime (I work from home) and fucking his younger partner Ben, when Joe works his night shifts.
I'm single again after my divorce. She discovered I was fucking a young bisexual colleague from work.
I'd taken a short video on my phone fucking him, and she'd seen it when spying on my phone.

Joe and Ben both didn't know that I was fucking the other. Especially Ben suspecting Joe as he acts so tough, but Joe came home early from his night shift a few weeks back, as I receiving a blow job from Ben in their lounge.
He could hardly begin to shout, so I invited him to join us. Joe fucked his partner from behind as I carried on feeding Ben my cock.
I didn't let on to Ben I'd been fucking Joe however, as he definitely didn't want Ben to know for some reason.
So now I get to fuck Ben with Joe in a threesome, and still secretly fuck Joe when Ben's not around.
I've asked Joe why he doesn't want Ben to know, but all he'll say is "Its just my thing".
It doesn't bother me either way, but I'd love to fuck them both when we're all together.