"Walk out on sb" is not a meaningful statement in English. Perhaps you meant " Walk out on the SOB" which is a somewhat vulgar statement statement typically used in anger to indicate that someone should stop tolerating the bad behavior of another.

To "walk out on somebody" means to leave (a room, a situation, or a relationship) before the person wants you to leave. It can be used literally, "I was in the middle of a sentence and he just walked out on me!" Or it can be used metaphorically: "We were married with two children and he walked out on me."

I'm not really sure what sb would mean here, can you please give the context?