threesomes??

alright so i’ve been with my boyfriend for two years now and we have a beautiful baby together. i’m bisexual and have been thinking about girls A LOT (🤤)lately and don’t know why?? anyway, he wants to have a threesome with myself and another girl cause he thinks it’s hot, which obviously it is. but i don’t want one just for the fact that i don’t want to see him fucking another girl. please tell me what to do.