The story format is easy to accidentally put into a runaway condition. I would heed Mizal's advice. It sounds like you are passionate enough to follow through, but let me expand on a few key things that may trip you up.
1. Each choice multiplies your writing if you are not careful. Compared to a linear story, each choice you add will add an entire additional story length of words. For example, if you are writing about three choices that can be made to save the human girl, then you have to write three full stories. They should all be different or people will complain that the choices don't matter and it is not a CYOA. If you planned for this to be 20,000 words on one branch of the story, three choices make it jump to 60,000 words.
This gets worse when you add multiple choices in a branch. Let's say you add 4 or 5 big choices and one branch expands to 40,000 words to accommodate. Factoring in the other two branches, you just planned a 120,000-word story. Now if you want to add "one more choice" you can end up around 160,000. Of course, not every branch needs to be the same length, but this is why the warning is valid.
2. People expect choices early and often. You might not have time to build an entire relationship before adding a choice. Again, there are ways around this, but it's tricky your first time. If you want to write a really good love story, it will take time to develop. Some kind of choice every 1,000-2,000 words is expected. If you just linearly write 10,000 words to build their relationship, people will think your story doesn't branch and complain that it is not a CYOA before they get to your amazing choices later on. Likewise, adding a choice between two options every 2,000 words (if not done carefully) can create 2^5 or 32 branches before you get to your time skip. This will create a problem with tip number 1.
If you take my example above and say that you are going to make their whole romance so that it ends up with two branches, then your story doubles to 320,000 words. You may not even realize your story expanded this way until you are 50,000 words in and realize that not even one branch is done.
You can play around with things and make the story work, but don't take this advice lightly. Maybe ask for more tips from people who have written lots of these. I wish you the best of luck with the story. It does sound like you put a lot of thought into it, and I think romance stories are very good when done correctly.
Here are a few key things that helped me:
- One page should be (roughly) 1,000 words or less.
- You can connect two pages with one choice that says "continue" but you should never do this for more than two consecutive pages!
- Not every choice has to lead to a new branch of a story. Some can immediately end it by killing your character (or getting them distracted, captured, etc). There are also ways to make choices that take you on a separate path that eventually funnels back into the same storyline as the other choice. You need to make sure each "mini branch" feels different enough to justify its existence but is never referenced later in the story.