my bf wants me to kiss another girl

hi eve. im in a big pickle here. my boyfriend has brought it up to me that he wants me to make out with another girl. he says he thinks that it would be hot seeing me kiss another girl and he would totally "touch himself" at the sight.. i have told him that i don't like the idea of even bringing another girl into that part of our sexual life/intimate part of our relationship. he said that it wouldn't be the other girl he's getting off to but the fact that his woman, me, is kissing another girl. but im still unsure about it and i don't want to share him in any type of way. WHAT DO I DO?!!!?