How can I be more secure in my body?

I just hate how I feel about myself. I have stretch marks and fat places. I think my face is ugly. I only look good with makeup. My boyfriend would probably rather be with someone else he just doesn't care to look. Or better looking girls don't like him back... this is just how I feel. I can't help it. My ex said I wasn't attractive to him anymore.
How can I be more secure in my body?
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