Help me understand

Hey guys so a few months ago I was working out a lot trying to get a good body. I took this photo and sent it to people both boys and girls on my snapchat saying I was proud of my body progress. When I told my boyfriend he flipped and told me I cheated on him. He's still not over it now and is insisting that if I don't admit I cheated he's gonna leave me. What do you guys think? When I took this picture him and I had been on a break in our relationship for a few days but it was short lived because we missed each other too much. Please please help.