They started from null, you are new, your game is new, i think be a bit more patient, advertise your game as much as possible, don't think too much about piracy - it's a way of free advertising. Who has the money he will pay, who don't have...well...someone earning 10000 per month, someone 200 per month. Beauty about piracy is that people will talk a lot about your game and the more they talk, better for you. Personally i'm going to recommend your game to everyone i know. Sorry i personaly can't suport you in monetary way, playing on crap pc, can't support myself...but will try to help on other ways. And if someone deserve support its you, and your game is even above DMD or BB, because of those realistic mature dialogs.
About engine hmmm it's not easy to know what is the best, look at the hummble expirience, elena's story or roundscape adorevia? They getting a lot, and all of them started from null, and all of them are done in rpg maker. My guess is that on renpy your game would be more fluid, but is it better to change engine...who knows?
If you keep the quality of game at this high level, ofc you will get much more at the time, also there is a one problem about your game, start is slow, what is great in my opinion, many just skip story to go to the porn pictures, maybe if you do some of them, as example, MC have at least one sex encounter with her husband or she spy on her sister or someone having sex, or scene with masturbation, BJ i think you will bring more people to your game. This - just to please those raw porn lovers.