should i be concerned my bf wants a threesome?

my bf brought it up and said he would like it if it was me and another girl but he disagreed with a dude instead. i’m very skeptical about it. i know he would never cheat too. he said he wouldn’t have sex with her and only eat her out while he only has sex with me. idk it jsut makes me very upset bc idk if i’m not enough for him. just the thought of me watching him with another girl makes me extremely jealous bc what if he finds her more attractive? what if he thinks she’s better? million of questions running through my mind. what should i do?