Cheating

Ladies i never go through anything of my finances. But he forgot to sign out of his email. He has started up a business in personal training at his own facility and i was checking into a certain business finance thing. I went to his sent email and I found a conversation with his ex gf he contemplated cheating on me but didn. This was about  5 months ago and I just found out. We are engaged and have a 14 week old baby. Torn if I should give him another chance