He’s right.
Justin isn’t to blame for this, it takes two people to make plans for two people…
She was fully aware of what she was doing the entire time, and the fact that the situation even got as far as it did makes me wonder.
Honestly, what I would do is the classic proverb.
If you love it let it go, if it comes back there you go, if it doesn’t it wasn’t mean to be.
Break it up with her, but not in a completely Iron Curtain kind of way, but rather under certain terms.
Tell her something along the lines of this “While situations like this are going on, I do not want to be a part of this relationship, let me know once you figure it out”. And stop talking to her and stop caring. Go out drinking and such. If she calls back and tells you that she will be good and will stop being in contact with him in this way, now it’s her own damn promise that she has to keep, that she came up with herself, out of her own will. That usually means something.
If she never calls back, it wasn’t mean to be, and just be glad it happened now, instead of later.