Boyfriend might be a cheat ?

So basically, this is going to sound very psycho but I swear I’m not xx I made a fake account and added my boyfriend on there and was flirting too him and he was flirting back. Not that bad but then he said there is nothing stopping ‘this girl’ (me) from sending nudes I then asked him about it like oh who’s this girl etc and he is still lying to me but I can’t say it was me because then he’ll know my fake account ? However he’s admitted to flirting with this girl but said it was his friend but ik it wasn’t as he was on his own and it was a photo of his room What do I do ?