OP I'm ashamed to say I did the gossip and collude behaviours with my DD about her DF. It was a huge comfort to me and to her AT THE TIME. Between 12 and 18 she really did not like her DF and made that pretty clear.
When our DD Left home at 18 for 6 months for studying, she came back changed. She told me how my "buddying" approach to her had badly damaged her relationship with her DF (true) how she loves her DF and if I don't that's my problem (true) how my "buddying" approach had left her with all kinds of learnt, bad behaviour that she was working through
I felt utterly ashamed. For a momentary sense of alliance and connection, I had betrayed both my DD and my DP her dad.
It is immensely to the credit of both my DD and her DF (now my ex, I left) that they have arrived at a loving, positive relationship that has nothing to do with me.
Don't do it, is my message from the other side. By bonding with my DD over her DFs irritating habits and (bloody annoying unfathomable) behaviours, I put their right to establish their own relationship at risk
Thank god they both overcame this. She is wise and he is forgiving.
(His behaviours were not abusive or mysogynistic - just fucking irritating, which was my problem)