My take.. on this.. may be different... as people all see things differently....

For me.. the friends that know I am DID... that I talk to... just keep talking when a "switch" occurs because they are uncomfortable - not me...

In e-mail.. alters seem to identify themselves - can see that by re-reading e-mails... this is with close personal friends..

Regarding "sex"... well... as the core personality... I would feel betrayed if.. my SO.. had sex with one of my alters... and didn't discuss it with me... a betrayal.. of sorts....to me it is not an "honest" approach in a relationship... and in the long run.. would most likely "bite" you... so if you want to keep a long term relationship.. if it is important to you..

including.. your SO.. core personality.. in the discussion.. about sex... would keep your relationship above board...and not "manipulative"..

as I said.. this is just my opinion....