How do I become Confident in myself & my body?

I’ve struggled with body confidence pretty much my whole life and just confidence in general. But I just want to be happy with myself and in my body. But how?

What advice would you give to an 18 year old plus sized girl who is struggling with loving her body & herself for who she is?

I want to be able to live my life freely and not always constantly think about how I look to other people or even my boyfriend in some cases.

My boyfriend has always loved me for me and I’ve always asked him, how? How do I love my body the way you love it?

Then I let my insecurities/ my head get to me and I overthink about what if my boyfriend is lying to me or what if he thinks other girls are way beautiful then me or have bigger breasts or a bigger butt.

How do I not let these insecurities get to me and ruin me and also my self esteem in my relationship?

I just have so much to ask every women whose been in my shoes, how did you overcome all of this?