How do I know she likes me and what do I do?

So I have this really good friend that I like a lot and we have known each other for at least 4 years. I can tell her almost anything and she won't judge me.I even told her I was bisexual and she didn't mind at all.I feel like she might like me cause she is really nice to me and she could care less about others (she's kind of a cold person sometimes).Also she hates sharing food and drinks with anybody including her best friend, but today I had a water bottle and I was drinking from it and she saw me and she took a drink from it too and it seemed like she did not care at all!I really do feel like she likes me some days but other days I'm not so sure and there is no way that I will ever ask her if she likes me or tell her I like her unless I am super confident she likes me.So could someone please help I would appreciate it.(and yes I'm a girl in case you didn't know)
How do I know she likes me and what do I do?
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