Your S15 is old enough to know his own mind. But your M is for you and W, not for him to judge.
He isn't your or W counsellor or MC. He is 15 and his brain like all teenagers won't be fully formed until he is 23 oR 24. W may see S15 as your agent or that you are triangulation or guilting W into an M she doesn't want.
She may say "it's time for me now"
V
Wolf, what she said. You can only control one person in the M, that person is you.
V, I wouldn't call you a WAW at all. I question how you got caught up with such a monster in the first place. I'm sure it is a long story.
IMO, a WAW or WW for that mater is very different from leaving a dangerous M/R.
But to your sitch, don't use your S as a pawn. If you are not, don't be tempted. 15 is an age where he knows what's going on.
Show him what a well-adjusted adult behaves like.
M 53 W 54, M since 98 D15, D19 8/2013 discovered EA, W maintained contact with OM until 10/14 7/2/17 W said she wanted S, 7/25/17 moved out of MBR 12/17 W says moving out 5/18, W still in home.