My 'dad' used to pull this crap. He's surely still accusing my stay at home mother who had two children (who would have noticed) of cheating on him their entire marriage. No. That was him. When she finally had proof, she took the brace step and threw him out. Best thing she's ever done for our family. We struggled at first, but it's entirely worth it.

Ahh, that classic "I'm cheating so you must be too". He basically told you that flirting is not where it ends. If he hasn't already had an affair, you can bet there will be in the future.