How can I become confident in myself?

Hey guys,
So my insecurities are really damaging to my relationship and I don't know what else I can do. My boyfriend, last night, told me that he’s getting really tired of my insecurities and it’s damaging both of our mental health. Every day and i mean every single day, i call him to talk to him about what he did wrong in the past. Why did you like these girls pictures, why did you DM her telling her she’s pretty, why did you follow her? Things in the nature and every day he says he is sorry and that he did it back then because he was stupid and had no idea what he wanted in life but he is no longer that guy and he’s changed for the better and he knows what he wants. he has reassured me that he is no longer doing any of that and he doesn’t want to ruin the relationship. He shows me his instagram likes and DMs and there is no liking girls pictures and no DMs from them. However, i still feel so insecure about myself and my relationship. Since my insecurities are taking over my head and i bring it up to him everytime we barely talk anymore and barely hangout. I understand him, if that was done to me I wouldn’t want to hangout or talk with him either. I just don’t know what i can do to make myself more confident and happy. someone, anyone please help.
How can I become confident in myself?
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