Sons new relationship

[PurpleMoose]

First time poster….
My (adopted son) has started dating a new girl. 3 weeks after his best friend ended with her. During the friends relationship with her, my son had massive concerns about the relationship and its impact, extremely needy behaviour, emotional manipulation, self harm, anxiety, eating issues and the loss of his job.
The friend has then got together with her best friend and started a new relationship days after ending the existing one. She now likes my son, and the friend has “give you my blessing to date her” and he’s going for it.
I have massive fears that his relationship with the friend is enmeshed and itself potentially toxic, he’s pushing the two of them to move out together, and I’m terrified of the impact this new relationship will have on my son.
She came over and couldn’t even talk to me and my partner.

Any experience of similar circumstances from anyone?

I would say to let it take its course, and make sure he knows you’re there for him. In my experience, having an opinion and verbalising it will only push him further in her direction.
Keep communication open, but with no criticism of her.

My approach in the last couple of weeks was to explain my fears, and that these are based entirely on what hes told us about her over the last 6 months whilst she was in the previous relationship with his best friend. I’ve explained that all I want in life for him, is to to be happy and have healthy and fulfilling relationships, and let him know that I’m always there for him if he needs me.
His source of advice unfortunately is from a friend that himself has extremely warped viewpoints on life and what healthy relationships look like.