Is this is a sign of flirting/ being crushed on?

This was back when I was high school. There was a girl whom I shared a class with, and there were a couple of moments where we would be the only two students in the class. This was when she immediately warmed up to me.

During the very first time the girl and I were in class together, she took interest in me and we had some friendly chatter. Often she spoke to me in the playful, teasing type of way a girl might do if she felt a certain way about you. Afterwards, during other moments, she seemed very happy to see me, with us hugging one another, even calling me sweetheart at one point, and there was a moment where she was staring at me while I wasn't looking, and she tickled my cheek, and my laughing made her giggle and say "you're so silly!"

Other cute times included one Valentine's Day, where I basically "dressed" the Valentine's colors (I was wearing red, white and black) and she gave me a hug (natch) and said "aww, you wore that for me?" and another where I could hear her telling a friend about how sweet she thought I was.

So basically, would any of you guys consider this behavior to mean the girl might have been infatuated with me? She and I never actually reached a point of being boyfriend and girlfriend, but looking back at it in hindsight does make me wonder, you know? Ultimately, I find this type of behavior towards me to be extremely adorable :)

yeah.. pretty obvious. as you wrote in your post she did A, B, C "as a girl would when she's interested in you" - so you arleady answered your own questions.

the only time it isn't true is when the person only does it in public, then goes cold in private. for females, that means they are triyng to get somebody jealous and to notice them that they want to be with, and your'e just the willing pawn to help them get that person jealous (without your knowledge.. cuz you're too busy enjoying the benefits of her affection).