How can I tell if a girl is being friendly or if she is interested?

I can never tell the difference.

some stuff that has happened to me with multiple girls that i barely know:

1. Girl i don’t know that well asks me if i have a girlfriend

2. one of them asks me multiple times why I’m so shy and nervous around her

3. one of them got very close and put her hand on my tummy.

Are those 3 flirting or just being friendly?

How can I tell if a girl is being friendly or if she is interested?
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