Can't help falling in love

I went to high school with a really nice and sweet girl. We've always been good friends but never written together. She has had a boyfriend for almost the entire time I have known her but when she went traveling from August to December 2016, she returned home single. When we met just before I went traveling, it was just like something happened to both of us. I suddenly fell for her. I then went to Australia with a few of my friends but her and I wrote each all the time every day.

Fast forward three months, I come home and hear that she has kissed one of my friends. For some reason I got really angry at her and broke the connection to her. A week later we are at a party together and suddenly we are both back with each other. She played with my hair, we held hands and almost kissed. The guy she kissed had spent the entire night with some other girl and as he was leaving he tried to kiss her but she rejected him and went over to me instead.

I've been told by many of my friends that they are 100 percent certain that "there's something going on". Yesterday at a party the same thing happened. We sat together the whole evening, held hands and at one point someone shouted stop kissing each other even though we didn't kiss.
I keep changing my mind about whether she likes me or not. Next Friday we are both going to a party. How should I handle it? See how it's going to go? Ask if it's mutual or just kiss her the next time I get the chance?