you can’t promise her that you’re not going to hurt her. you are going to hurt her, that’s what humans do. we hurt each other all the time. you’ve probably already hurt her at some point, but you can’t really control that.
what you can promise her is that for the time being that you’re a part of each other’s lives, for the duration of whatever kind of relationship you choose to have, you’ll make her happy. that’s all you can say for sure. and I promise, it’ll be enough.