Advice on admitting feelings to an ex-friend

I graduated high school a couple of months ago, and I, a female, was friends with another girl for a year and a bit. During that time, I developed a crush on her ( she is straight) and obviously tried to suppress it. However, towards the end of our friendship, I began to display behaviours that you might when you like someone, such as asking why she would leave my messages on read and frequently asking if she was okay. Obviously, this would have been overwhelming for her, despite me doing it from a place of care, and she ended the friendship last year in January. We still attended school together for another year, and seeing her every day didn't help the feelings I had for her. Fast forward to now, and it has been over a year. I still find myself thinking about her, despite trying every method I can think of to stop. I had wanted to tell her in person on the last day of school that I had feelings for her, as it had been on my mind for the entire year, but I never got the chance. I really do not know what to do. I have been thinking about texting her and telling her how I felt, and how those feelings may have contributed to the friendship ending, because it hurts knowing that she may never have realised how much I truly liked and admired her. However, I do not want to come across as strange. At the same time, I have tried everything to move on and I keep coming back to the feeling that I just want her to know. I have not spoken to her in over a year and the only that connects me and her is a mutual friend we have.