Sex scenes in fan fics

Argh. I need to continue my Synack fic, but it would mean writing sex and I'd feel really awkward doing so, like I'd be over stepping some sort of boundary, you know? But I don't know what else to write and the only other option would be abandoning the fic completely, which I don't want to do. I don't want to have someone else write it either, because I want to write this 100% by myself and I also don't like working with other people, I don't know why. That's just how my brain works for some reason. Someone please help. I don't even know. .-.