I always struggle with telling if a new friend is genuine or not?

I keep getting myself in situations where I become close with a friend for 3-6 months. Then realise they are actually a frenemy. I get so deflated and disappointed and looking back it was so obvious but I can't see it in the moment.

What are some ways to tell when forming new friendships if they are good for you or not? Apart from obviously bad stuff.

I always struggle with telling if a new friend is genuine or not?
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