Appearing this week on “The Tonight Show With Jay Leno,’’ Bobby Brown performed a song from his forthcoming CD, and it was about his late ex-wife, Whitney Houston. Called “Don’t Let Me Die,’’ the song includes the lines: “I didn’t realize that every breath I took was from you. You were my air.’’ The Roxbury-bred singer’s new album, called “The Masterpiece,’’ is due out June 5. (It will be his first CD since 1997’s “Forever.’’) The former New Edition singer and Houston were married for 14 tumultuous years and had one child, Bobbi Kristina, before finally divorcing in 2007. Houston died in February at the Beverly Hilton in Beverly Hills. Clad in black leather and wearing sunglasses, Brown sang: “I guess I [messed] up pretty bad/ I didn’t know who you were/ I didn’t know what we had. Now I’m stuck living in the past/ Trying to get the pieces back/ But I guess now you’re gone.’’