Um, note that actually in Japan, shounen-ai actually refers to boyxboy relationships that are more...explicit in nature. It's a common misconception overseas that the term is considered to be "lighter" in nature and people are generally unaware of the Japanese term for it which would be katakana-ized "Boys Love" and often shorthanded to "BL".
The girl counterpart of course would be "Girls Love" and actually not "shoujo-ai".
Wikipedia terminology note:
Quote:
The term shōnen-ai is no longer used in Japan; the wasei-eigo construction Boys Love (ボーイズラブ, Bōizu Rabu?, but usually rendered as English, occasionally spelled Boy's Love or Boys' Love, or abbreviated BL) has largely displaced it, due to associations of the original term with pederasty (which were not associated into English usage). Ironically, the similar English term "boylove" has the exact meaning Boys Love was coined to avoid.
As for the het relationships, I honestly have no idea.