Were Doug and Brenda fu*king?

Possibly. However it's more likely that Doug was just perving on a younger, fitter, more tender, not to mention tighter model than his current one.

If they weren't then.............they are now

No; they weren't, but Doug was looking; Brenda was a very pretty girl, but then so was his wife. Lynne noticed Doug looking at her sister as well, and while she didn't seem to like it, she didn't say anything to him. It was just a look.

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I dont think they were, but who could blame Doug for thinking about it.

Kind of hard to not think about it.

State champ in martial arts, trained with firearms, I eFF'n dare you!