When two women (especially hot women) get intimate with one another it is a truly beautiful event. Even if your only involvement is watching as it all unfolds.
The oportunity to see two women, at there most beautiful,(and as nature intended, ie. naked), pleasing and enjoying one anothers bodies is, in my opinion, one of the standout occasions in any males life.
So I say your boyfriend was a very lucky man, However I do hope, you did it for the right reasons and no drama resulted. Any experiences of my own have occured in the company of close friends or strangers. Never with a partner involved.