How do I (can I) trust again?

We have been married for almost 15 years. The entire time I thought we both came into the relationship as virgins because he told me repeatedly that he was. Last night we had the sex talk with our two oldest and during this they asked questions that led to us talking more later when we were alone. Before we started dating, he was dating a girl for a while, but has always said that nothing ever happened besides oral. Then he casually says "I did her in the butt with a condom". When I said "I thought you were a virgin and that's what you have always said" his response was "well, I was. The butt doesn't count." What?!?! He is insistent that he only did her from behind and never in her vagina. Im not buying that. Why would he do one and not the other? I'm not surprised that they had sex, I'm just pissed that he has denied it all this time and now it comes out. Why wouldn't he have just told me the truth? I have always assumed something happened. Over the years there have been several times where he has lied to me about various things. All of which are relationship/sex related (not sure he didn't cheat on me when he was away for work- he of course denies it). I love this man with all my heart but I'm not sure how to handle these things. What to think of them. Because of his job, we move a LOT. I have been a stay at home mom for 11+ yrs. I have 3 kids. Had a miscarriage in January that he didn't even seem to care about. Never an I'm sorry, hug...nothing. He was in school again and it always seems to trump family. There have been times when I feel like throwing in the towel, but it scares me. I have to think of my kids. Every time I think we are at a better place, something else happens. I am giving it my all. I have always been 100% honest with him about everything. I just want him to understand how this all makes me feel, care about it and make things right. For the past year and a half we have been trying for #4. Now I'm questioning that too...