How can I help myself become secure within myself?

Hello everyone! I am 33 years old and I am very insecure within myself and i have no idea why. I know i’m pretty but maybe it’s because i know i can be a mean person? I don't know. anyway, i always think that my boyfriend is talking to other girls and i want that to get out of my head. So a little back story, we met in Nov of 2014 and dated January 2015 but he was still all about other females and i had no idea about it until two years ago. He was still liking girls pictures, DMing a few girls telling them they were pretty. he stopped liking their picture and DMing them three years ago. I found out that he did because i was looking through his phone one day and saw his liked pictures from years ago and it was all bikini girls. i asked him why he did that and he said sorry but he wasn’t sure of us back then but now he is. i said okay but i still think about it and i feel like he will still do it if he had the chance to. It’s been a non stop issue for years. I don’t call him for anything positive, i call him to ask him if he still is liking pictures and he will tell me no and to please stop because it is getting annoying. today i called him to check up on him because he is sick and then i asked him so is he still talking to this specific girl and he said no and then i told him “i have a feeling that you are.” and he said no he’s not so i continued with it for a while and he got mad and said “not even when im sick that you can drop it, you are an insecure piece of shit. You are so annoying, this is why i don’t call you anymore because all you want to do is complain and bring up the past. stop calling me” and then hangs up. i know im going to stop calling him but it makes me sad because I don't know if i stop calling him will he call me. anyway, my original question is “how can i help myself become more secure within myself?” thank you in advance
How can I help myself become secure within myself?
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