About smut:
personally, the writing and reading of smut makes me very uncomfortable as well as scared, slightly. I'm very sensitive when it comes to sex
because of that, if I were to ever have sex in a fanfic of mine (I never would in my own book) I would probably just get someone else who likes writing it and collaborate with them for the certain chapter(s) just so I'm not made uncomfortable, but the story still reads like a cohesive whole.
also, I would never put in sex unless it seemed appropriate for the story
I'm not sure what I mean by this, but basically, if you don't think you could write smut up to the standard you have in your head, a little help in writing it from someone else would never hurt, especially if writing it is stressful for you or makes you unhappy/uncomfortable in any way 
(this was kinda off topic, and also not really related to the actual problem, but I just felt like I should say this)