wtf is happening, who is wren, why is he calling him ba by? aaaa?

If you remember Tristan backstory he was that vampire

if you come back some chapters there's a little backstory talking about wren and tristan's past

Ren took care of Tristan after he killed his father. Wren took care of him as his own child.

ohhhh i must’ve forgotten, im gonna find it thx guys