if the friend asks you to stop giving advice, then the best way to help them is to respect their wishes. continually trying to impede on what he feels is his best course of action whether it is or not is going to be an obstacle in your relationship going forward because essentially you are not respecting what they are asking you to do.

It may be hard to back off but when it's been overtly requested from the person you feel you need to help you really have no choice but to let it go.