I think I would have said "If you are in a situation where you think you may not be able to keep your promise, talk to me about it first and we'll try to solve it together."
I don't know if that would work, but it seems worth a try.
This was a nice conclusion to a conflict brought up last chapter that I wasn’t too keen on. I do feel like he could have said something like “I’ll never hate you; being mad at someone doesn’t mean you hate them”. She doesn’t seem to understand that getting angry at someone and hating them are two totally different things which could leave to her leaving arbitrarily. It just seems weird me that he wouldn’t correct that when the misunderstanding could lead to her killing herself. Also a rope as a symbol for them climbing out of the depths together is probably not the best symbols (considering the noose), I guess unless the author thought it was better for the double meaning (not good with sysmbols)
It's good to bear in mind that, while Taku is literally very thoughtful, he developed that thoughtfulness in the context of an autistic-spectrum disorder. The result is that he handles some psychologic issues far better than do most people, but sometimes does rather worse than would many people.