Break up while pregnant?

My boyfriend and I were only together about 4 months before I got pregnant... A month or two ago I had a gut feeling he was cheating on me but had absolutely no proof. When I confronted him about it he'd deny everything and make me feel crazy for even thinking he was cheating. The intuitive feeling just kept getting stronger so I looked in his emails. He had been emailing his ex, whom he was with for 2 years before we got together, telling her he loves her and all that. 
I'm 5 months pregnant and absolutely heartbroken. I don't even know what to do. Anyone have experience breaking up while pregnant? This is such a nightmare.