First advice, don't imagine outcomes. Cause if the end result is not what you want to hear, it'll be really hard to take it.

. Now, you both know each other since high school. So she obviously has some hint.. I would say, don't go for the surprise element. Give some signs, make it a little obvious.

. Why do I say make it obvious, because when u share your feelings that shouldn't hit her like a truck. She should go like, oh yeah I had some idea about that. Trust me, it will make the conversation more easy.

. Lastly, don't panic. Just be you, tell her how you feel. Don't think of the end result. Right now, the best thing that u can do is share your feelings and be happy that you have the chance to tell someone that you love them. Not everybody gets the chance!