The agreement between you and your FBuddy that you will only sleep with eachother.
Yeah we date other people, but Hook and I only sleep with each other - we're sexclusive. :)
Having sex with only one person, yet not dating them exclusively. The ability to date several people while having an understanding with one in particular that you are their only sex partner.
I couldn't have sex with Tito last night because Mike & I are sexclusive.