Chances are your friend was depressed prior to the relationship, else he’d have left a toxic relationship already, no?
Oh you sweet summer child. The thing about abusive relationships is that for whatever reason, people find them hard to leave. Even when the person is literally beating you, victims feel some sort of undefined pull that keeps them in place. They often rationalize their partners behavior and in the worst scenarios, they start to believe that they somehow did something to deserve this abuse. It's horrifying to see a friend undergo this transformation, and it's also incredibly frustrating when they refuse to do the obvious steps to help themselves.
The best analogy I can think of is drug addiction. At some point you know it's bad for you, but you keep going at it because you literally can't control yourself anymore.
The reason why I tell you this Hector is because it can happen to anyone. Even you. Not enough people are aware of the dangerous pull of these kinds of relationships, and even those who are aware can still get sucked in. The only real defense is to spot the red flags and get out before you cross that event horizon.
I am aware of this, moreso than most.
If your friend stayed in a relationship that was obviously abusive to an external party within two months of it beginning, it is likely your friend had some issue prior to the relationship. This could be from their ignorance of what a healthy relationship looks like, but if you were pointing out the issues you saw, it is much more likely they were emotionally incapable of committing to ending something that’s harmful to them.
Depression is an insidious beast, it manifests itself in so many different ways it can be difficult to identify, even if you know it’s there. It doesn’t even have to be bad to be wholly destructive to whomever has it because it can affect so many things in their life that it’s like death by a thousand cuts.
If this relationship uncovered they had it, the relationship was good for one thing at least, because now they can deal with that.
Regardless, the latter point still stands: you can lead a horse to water but you cannot make it drink. Your friend lives their own life, all you can do is be supportive of them until they make the decision to leave the relationship.
The fun part about abusive relationships though is that even if the relationship is ended, it doesn’t mean the abuse stops! Yay for extra trauma on the side.