... if it isn't about sex, don't have sex with a married man until he's divorced, then nobody will call you names ...
Beautifulmelody has been roundly denounced for using 'bad' language about the OW whose affair with her father caused her and her family so much distress, but in my opinion she's hit the nail on the head here.
Respect the contract. Respect the family. Even if he's so (trend/bored/abused/ready for out/entranced with you/insert whatever pressing reason) ... that doesn't mean to say you have to have sex with him until he's decently free.
We are supposed to be civilised and not ruled by our baser instincts. What beautifulmelody has raised, and I applaud her again for doing so, is how it's the physical relationship that is so hard for the family to deal with. And it's never fair to ask them to. There is no justification ever for that.
If, after divorce or obvious separation (to a different house), Dad shows up with a gf, that would be hard, but everyone would have to get on with it.
I think beautifulmelody's point is that if you behave with disregard for the pain and humiliation and shame you're causing to others, then you get what's coming - if they want to be rude about you, so be it. You gave up your rights when your knickers came off ...
Of course, it's not great for beautifulmelody to be angry like that, it won't help her, and she's going to have to resolve her feelings and find peace again some time, but there's no way we can defend the OW from her anger.
Having sex with a married man is always, always playing with fire.
And some of us see it as a line never to be crossed, and some of us don't even see the line. Until people start shouting and calling names. And then instead of apologising, we say well who cares about the line anyhow? But that line is there to keep children safe and protected from the turbulent world of adult sexual feelings. Cross it, and you end up hurting them. Beautifulmelody is a hurt child.