I just double checked to be sure, the only way you can lose Melanie's path is if you don't go find her in the changing rooms. It may sound counter intuitive but she likes when you're direct and make a move.
I'll look into it, the early content contains many path ends that in hindsight were excessive. I'm working on removing these while making sure the story still makes sense without them. If you still aren't able to stay on her path, my discord has a walkthrough made by one of my mods that could help you.
Speaking of excessive path ends, I found it funny how Jessi is meant to be this "has crush on MC" sister character, but if you aren't a perv with her once that's enough to lose her route. If someone's interest runs that deep it should take a stronger, direct rejection to end things!, is what I felt haha.
Far from being a game-killing thing, but if you could someone rework how her route develops, so it doesn't go down like that, I really feel it'd be strongly in the game's favor!
That's one of the things I'm planning on fixing, I want to make it so that she is more persistent in her chase with the MC. I will be fixing some of the glaring issues in the old content for 0.5 and improving the quality of some of the writing, but because I'm focusing more on other improvements for now, the big changes for old content will likely be in 0.6. It won't change any of the story, it will mainly fix problems with the design, visuals, show off the characters' personality more in their dialogue, and improve how players experience the content.