You’ll notice a trembling excitement in him when you explain your expectations in this arena. No doubt he thinks male lesbianism equals male heterosexuality. It does not. Male lesbianism is almost exclusively oral in nature and very demanding on the submissive partner, which he most certainly is. Hours will be dedicated to servicing his mistress with very little if any reward for him, other than your smile.
Tip: It is not unusually for teenage girls to form harmless attachments and it is a fine way for your sissy to explore his ‘lesbian’ side. Pair him off with another ‘girl,’ perhaps borrowed from a friend, for practice lessons and insist the two become a couple for a period of time. Innocent petting, fondling and kissing should be insisted upon as a precursor to more intimate forced bisexual experiences to come in the future.