As far as a specific biblical passage, I'm not a bible man, so I can't help you there.
But - I often have to teach Kantian ethics, which (among many other things) often comes down to a basic point - namely the golden rule (do unto others as you would have done unto you). When you talk about the Golden Rule using Kant to evaluate a behavior or decision, you then talk about reversibility (would I be willing to have the same thing done to me under similar conditions/circumstances?) and universality (would I be willing to have the logic behind my action become a universal law for human behavior?).
My favorite example of this is from a student of mine who has a twin brother. One night, his twin brother got trashed while driving, and flipped his car, 5 minutes from the brothers' apartment. Knowing that the cops were on the way to check out the accident, the drunk twin called the sober twin and frantically asked him to drive over to the scene and take away the open bottles of beer.
I love this example, because from a morality standpoint, the sober twin has a really tough call her. You have to put yourself in this guy's shoes and think about the fact that this is his twin, and his twin is facing some serious criminal charges, etc. It would be tough to ignore this call for help - especially if this was a one time thing.
But - let's break out reversibility and universality and see what they have to say.
According to reversibility, it is interesting - would the sober twin be willing to place the drunken twin into a similar situation? This is an important point, because if the answer is "no" - this suggests that one person in the relationship is taking advantage of the relationship. This is why domestic violence is evil, even though the abused person often claims that they can handle their partner's abuse or that they don't care. It's one thing to argue that you don't care if someone abuses you, but, you can get a person to see that they are accepting behavior that they, themselves, would never impose on someone else.
And - this really breaks down with universality. While it is all nice to help one's brother, etc., think about how horrible the world would be if - every time a person got into trouble, they could call a relative and ask a relative to do something extreme/illegal to bail them out. If this became a universal law, the world would suck. You would live in a world where, at any moment, one of your relatives could call you out of the blue and demand that you incur a tremendous personal sacrifice because of their indiscretion. And - in this world - if you were a victim of a person's indiscretion, the evidence of this harmful behavior would probably be "erased" by the perpatrator's relatives. And - the thing is - we know "some people" who actually do this - and it's horrible. Who wants to live in a world where people can do whatever they want because they have a friend or relative who can bail them out - no matter what.
Sorry for the long discourse, but, I went off a bit because I think you can have a similar, interesting discussion with your friend. Is he accepting demands from his buddy that he, himself, would never even think of imposing (reversibility)? And - is he accepting demands from his buddy that are far beyond what one could expect a "good friend" to do (universality)?
The most important thing here is the idea of a relationship. A relationship must have an even amount of give and take in order to benefit both parties. This is why the golden rule is so powerful. It forces you think about how your actions/demands/decisions affect the people who are most important to you, while - at the same time - demanding that you think about how the actions/demands/decisions of others affect you.
Good luck man! (Sorry for the long-winded response) This sounds like a tough problem....