Advice on how to stop overthinking and how to boost my self esteem.

I am in an incredibly healthy and happy relationship. But, I tend to overthink things due to my past relationships that ended horribly, in which has also caused me to see myself as not enough for anyone. My boyfriend treats me like a queen with the upmost respect and kindness, always ensuring that I am happy in all aspects especially emotionally since he is aware of my past. But I always tend to overthink eveything and feel insecure due to my past. How can I help myself overcome this feeling when I am getting support from everyone around me, but my thoughts wont stop creating dumb scenarios where I am not enough for anyone?