How to get rid of negative thoughts?

I have been in love with a bitch in the past who lied to me about loving me because I was good to her and now, I think everyone is a bitch.

Now, I am into a girl but I just can't stop these negative thoughts that she's a lier. She is good but I just don't trust her. No matter what happens, a negative thought comes to my mind.
I really don't wanna fuck this up.

How to get rid of this negativity?
How to get rid of negative thoughts?
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