Totally agree with you.
Cary is in desperate need of therapy, not just the occasional chat with Dr Travis. He has the same demons as Gideon and Eva. I think Gideon will pay for treatment/rehab for Cary, hopefully getting Cary back on side. Gideon knows if Cary is in a good place, Eva will be happy.
Just a thought.
In "Friends" Joey was the third person in Monica and Chandlers marriage. I can see the same happening with Eva and Gideon, with Cary.
Eva mentioned to Gideon that Cary was for life.
He just needs support, love and someone to point him in the right direction. Helping him stand on his own two feet, to be independent.
He got worried when Eva mentioned going to Las Vegas, he thought she was going to tell him she was moving in with Gideon. He has to realise, this will happen one day.