Someone who reveals all their emotional baggage to anyone who will listen. Relates to someone who talks about all their problems--especially in dating and love--on a first date.
Sarah and John will not be going on another date because she was an emotional slut on the last one. She told him all about her failed relationships, problems with her boss, and how her cat keeps throwing up. She cried; he left.
An emotional slut is someone who has feelings for more than one person at the same time. Like a regular slut sleeps with several people at once, an emotional slut may be in love with several people at once.
Amy: Christine is such an emotional slut.
Jenny: Umm, why do you say that?
Amy; Well she actually told me that she's in love with Josh...And Kyle. At the same time.