Are the two of them actually having an affair? I got the sense that there was mutual mostly-unspoken attraction, but not a full-blown affair.
One thing I didn't love about the play is that, after the curtain falls, a lot of innocent bystanders in the family are probably going to pay a heavy price for the lead's actions. It's a little bit like what probably happened to the nuns who sabotaged the car at the end of The Sound of Music. Maybe that's part of the playwright's point, but it's not as well-developed as it could be.