Am I over reacting?

I’ve been with my boyfriend (now fiancé as of Christmas 2018) for 6 and a half years, and we have a child together as well that’s 4. We’ve broken up a few times for a few months at a time due to him being uncertain about “what he wants”. We’ve gone through constant hardships in our relationship and I’ve supported him and his sobriety a long time. Last night, 6 days post engagement I’m on his phone searching up someone we went to high school with he’s friends with on FB so I could see his page for photography as a potential candidate for our wedding pictures. When clicking on the search bar I see he’s searched his ex girlfriend on Facebook very recently. And also watching porn (when we’d had sex that night or night before - he’s not deprived by any means) Now he has only romantically been with 2 people in his life - me and her. He was with her for 2 months before he met me and she cheated on him and dumped him. Anytime over the last 6 years we’ve temporarily split that’s the first thing he does is add her on Facebook and try to talk to her. She is a completely different kind of girl than me. Skinny and blonde. I carried our child with this body of mine, gained weight. Lost it. When he didn’t want another I went on BC that caused me to gain 70lbs putting me at my heaviest ever, he wanted a baby I had to take infertility drugs that caused my hair to fall out. I hate myself and my body and I express to him daily the depression and anxiety it causes me. This was just a slap in the face. I’ve taken off the ring and told him I’m done. I’m crushed. How could you watch someone you love plan your wedding and be filled with excitement while you’re apparently still honing over your ex? I love him, but this has been a shot at my self image and what I thought was a trusting relationship.