In your sentence, Ditch word is used as very popular slang in meanings like "to get rid of", "to get away from" or "to discontinue association with". So here Ditch is used in meaning of leaving someone. That's gets your sentence translated into easy words as "Don't leave me", "Don't betray me" and most closely "Don't cheat on me". This sentence is usually used when someone is betrayed by someone in competition, in business or in emotional relationships like friendships etc.