Chelsea and Charlie broke up because he has slept with her best friend, Gail.
Chelsea Melini is played by Jennifer Bini Taylor, first appearing in Season 6 Episode 8 as one of Charlie's one night stands, although after her first episode Chelsea does not reappear until Season 6 Episode 15. They fall in love and she is the first woman that Charlie ever says the three words to.
Chelsea Melini appears in the show until the end of season 7 and then does not appear until the beginning of season 9 where it is Charlie's Funeral where she mentioned that he gave her an STD. During the time between them meeting and Charlie's death, they are exclusive for her time in the show and they break up at the end of season 7.
The long-running show Two and a Half Men has made it through twelve seasons and significant cast changes. The show powered through some negative criticism and came out as one of the top comedies ever. Check out these 16 fun facts about ‘Two and a Half Men’ shared by Indiatimes.com.