Per wiki policy, Spoilers Off applies here and all spoilers are unmarked. You Have Been Warned.
Balthazar's connection to John is...
- That he was one of the demons who noticed John seeing their true faces and tormented John for it to the point that John killed himself.
- That he was a past lover of John's, like how Ellie was going to be before her scenes got cut from the movie, which would explain the Ho Yay.
- That he killed a past lover of John's. Or a family member. Or a friend.
Isabel was manipulated into killing herself specifically to fulfill the Evil Plan
If Isabel needed to be in Hell and Angela on Earth in order for Mammon to successfully tap into their connection as powerful psychic twins and possess Angela, then it seems quite likely that the villain's minions would take to emotionally and psychologically manipulating her at the mental hospital to push her into killing herself and condemn her to Hell. As Isabel was Catholic and would not have killed herself specifically because she'd know she'd go to Hell for it, Gabriel might have talked her into it, using the fact that they are an angel to gain Isabel's trust and convince her into doing it. The reason God stripped Gabriel of his power was not because of his collaboration with Mammon
It's because he directly killed Chas, taking an innocent life and breaking the rule of the balance. Constantine 2 will set up Justice League Dark
Constantine 2 will play up or make John's bisexuality more explicit
The movie doesn't confirm if this version is straight and received Adaptational Sexuality, so it's safe to assume he's bi like his comic counterpart. Maybe we could have a few scenes where John flirts with another guy?