Alright, I played through it.
I'd probably have gone with Ren'py. The game seems slower than necessary, and a bit clunky. Since you're going with a VN anyway (Unless you plan to add gaming mechanics), it might not be a bad idea to change over. The coding is relatively simple.
I'd probably rethink the animations too. The sloppy toppy scared me. I'm not sure why, but it left me shook. The sex wasn't bad, though.
I'd also work a bit more on the dialogue. I'm not sure if English is your first language or not, but maybe get a friend to help you make things sound a little more natural.
Still, it wasn't bad, and people might hate AI art out of some moral obligation - But I totally get using it. Not everyone has the money to hire an artist, and if you have an idea - and the means to make that idea a reality -it would be stupid not to use it.
Still, work on optimization and dialogue. Him choosing THAT moment to read the letter doesn't make sense from a storytelling perspective. Might be a good idea to give him a good reason to hold off on reading it, or work a different avenue into it.
But that's my critique. The reptile can fertilize her eggs with me anytime.