To dream of a condom symbolizes thinking patterns that are counter-productive to goals, objectives, or attaining what you desire. It can both good or bad depending on who is having sex in the dream and what qualities they symbolize in you.
Positively, the condom may reflect your attempts to prevent emotional pain. Negatively, a condom may represent negative thinking patterns that hold you back.
Since sex in dream is usually symbolic of merging personality traits that create life experiences, a condom symbolizes something you are thinking or doing that prevents that from happening.