I agree with everyone here; you did NOTHING to cause this, you did not deserve this and your inability to not 'see' what was happening is a reflection of your kind, big heart and faithful, generous self.
I agree with upping the IC. Searching for keywords such as 'trauma-informed therapy' was the key to finding my best therapist. And don't be afraid to go two or three times a week in the beginning... you have a lot to unpack here and that is what they are there for. I also second Butterfly's suggestion of getting into your GP to discuss the impact this stress may be having on you physically.
Now, for H. I hesitate to even delve into this because in so many ways the best approach is to not spend an iota of a second 'untangling the skein' of your H's behavior. But for me to reach my own acceptance and approach closure (I'm not fully there yet), I found that having some understanding of what might be happening within him was helpful for me to let go. Early on in my situation, during a brief reconciliation, my H told me that I made him feel extremely guilty and shameful. Mostly for his traveling lifestyle and not being there for me and the kids. Which was so perplexing to me because I had no resentment nor anger for his travels, even during high-stress times (alone with a newborn and three other little ones for a couple weeks for example). I felt like we were a team and we both were pulling our weight in different arenas towards the same goal. But looking back, I realized that his guilt and shame came not from me, but from within him. He had likely been behaving in ways while he was away to feel guilty and shameful about. And so long as he was able to compartmentalize these behaviors, he could function. But once the mask came off, so to speak, he fought (and is fighting) tooth and nail to justify his life and choices by vilifying me.
I find it really hard to believe that all my life to now was a lie. That these beautiful children born in love, that all those moments of unadulterated joy and connection between me and H, the success we achieved together, the huge network of loving friends and family, was all a ruse. I don't believe it was. I truly think that when H was with me and working towards our goals, he was happy, he adored me, he was in love with me. But he has an ability to compartmentalize and be more than one person. He could be all those things to me and in our life, AND he could go off on his work trips and be a completely different person. Maybe he self-soothed by telling himself that flirting with female clients would get us more jobs and therefore be a benefit to me and the children. Maybe he told himself he 'deserved' to indulge in some act or another because I was 'unwilling' to provide him with what he needed.
And which of those lives are the real one and which is the fake one? That can't really be answered, but I put it out there that his life with you was just as real as the double life he led. But you don't want to be married to half a human or a split human. You want to be married to a whole person. It takes a very un-whole person to live double lives to that degree.
I say all of this not to be generous to your H, but to implore you to be generous with yourself. You did all that you could with the information you had at the time. What you do with the information you now have is of greater importance than what you did when you were kept in the dark during your marriage. By that measure, you are doing fantastic.
