My boyfriend found an old picture of me on his friends phone (nothing inappropriate, my stomach was only showing) & Now he thinks I don't care about him or Love him. What do I do? Its ruining my relationship ):

You don't, you can not and should not even try to "prove" you care, often guys try and use that show me you care, crap to try and talk girls into having sex.

If someone has a photo of you, it can be a old boyfriend, we all have and will have them over time ( or girlfriends) it happens. He is being immature and showing he is perhaps not old enough or mature enough to be in a real dating relationship.

You break up with him and find someone who is more secure about themselves and are not jealous. If something this small creates such a drama queen out of your boyfriend, what do you think will happen if something more serious was to come around.

What's ruining the relationship is his own insecurity, and immaturity, not some old picture. Leave him alone and see if he grows up, or gets over himself.

You are the one who should be mad... at him!