When she first found you after the "accident" at the lab, your initial thoughts where that you'd be safe ... she did take good care of you after-all, feeding you, giving you a safe home to stay ... and the few times she sat down to talk to you, some company.
But your wife, and colleague soon began to feel "neglected" in ways you simply couldn't satisfy her any longer, seeing as how disastrously your attempt to allow her to use you as a sex toy turned out, nearly breaking your bones ... she came up with a solution, not exactly one you liked, but nonetheless one that would make her happy ...
After all, you were still with her, and you thought it'd be selfish to disregard her physical needs ...
That night, one of her old friends, probably an ex of hers too by the way they immediately started bonding with each-other, reminiscing old times, passed by your place, as she sat you down to introduce the two of you to one another.
However the pleasantries stopped as soon as he began undressing, and with little to no say in the matter, you were thrown to the ground as your wife smiled and simply laid her foot down, firmly pinning you in place, and forcing you to witness their newly revived relationship.
You'd become the third wheel in a threesome, however not as an able participant, but solely as a spectator. A cuckold ...