Heartbroken (really long)

31 weeks and 3 days pregnant and my fiance just broke up with me. I'm so heartbroken, and don't know what to do. I'm already in therapy because of severe depression and anxiety. I'm so lost right now. I have 2 other kids. They are not his biological kids but love him, and he's walking away. After finding out I was pregnant, we got into a financial situation that has me living with my parents until we find a place which will we be moving shortly after our son is born. This is a high risk for pregnancy and I've been nothing but stressed. For the last few days we've been in a really bad place because I didn't tell him the full truth about a part of my past. I was ashamed and embarrassed. I didn't just not tell him, I just didn't tell everything. I was 18 in a horrible family situation that I needed to get out of. I am now 25 and nowhere near who I was. We were finally getting past that. This morning I get a call at almost 5am from him about Facebook. FACEBOOK!!! He going through my page and saw that I had searched my ex best friend (guy) on 2 days. I only remember one day, and that's because he wrote me apologizing for ruining our friendship and congratulating me on the baby and engagement. I never wrote back. Didn't even see it until my fiance said something. It was a different name on Facebook, so I searched the name, saw who it was, explained the message, deleted the message and blocked this person. No problem. But now it says I searched him on 2 days instead of one. I'm not saying I didn't cause it's right in my search history. I just don't remember what made me search. And because I don't have an answer he thinks I'm lying and hiding things when that's not the case. And he's leaving me. I don't want to lose him and wouldn't do anything to lose him. I understand I'm wrong for withholding details from my past (years before I met him), but I've never cheated or even thought about any other man since I met him almost 2 years ago. Even while he cheated and disrespected our relationship I never strayed from us, didn't even think about. But now everything is ending because I can't explain a Facebook search. There's been plenty of things he didn't have an explanation to, but really over a search? But he couldn't explain the condom wrapper I found a few days before our anniversary. I could see if it was a message or something but a search?? How do I get through this? This is the love of my life. What can I do? I need him to understand. I'm losing it right now.