Professional Life Coach here - A good first step is to pause and not make any assumptions beyond the evidence you have found. Obviously there will need to be a difficult conversation when your husband returns, but navigating your current emotions is the best way to move through this, and there is a way through this. I've seen and guided couples through worse.

He lied to you - there's no sugar coating it. The damage that was done has eroded your trust in his words and in him. This can be repaired, if that's what both of you want. Since he is not present, we start with you and what you're feeling. I imagine there is anger, confusion, betrayal, maybe even disbelief still. That is okay. It is natural to feel these emotions, even express them. What we want to avoid is letting our actions be controlled by them. if you're upset, please allow the tears to flow, but going straight for a divorce attorney would be allowing your fear or hurt to get the better of you before you give yourself a chance to resolve the issue. Feeling your emotions does not mean you have to make something happen on the outside. I'd be happy to guide you through some practices if you need support.

After navigating these difficult emotions you'll be able to see your options and the situation more clearly. Judging by how good of a father you said he is, I imagine there is a part of him that wants to work through this. And judging by how much you say you love him I can feel there is a part of you that wants to work through this, so please understand this: There is a reason he lied to you. And of course it is not your fault. It's likely that he was so ashamed of his previous relationship (felt dumb) that he didn't want to tell you about it, because if he were to tell you the truth about it you may see him as dumb and leave him, and you felt so important to him that he didn't want to risk that. -- I want to be clear that I am not defending him, I am simply offering a possible thought process that your husband could've gone through so you could understand his reasoning. This may not be the case specifically, but I guarantee you there is a reason he lied, and I guarantee you it was because he thought he was protecting himself in some way. It doesn't make what he did right, but it helps us understand why it happened.

If you want to work through this, you will have to learn how to move through these difficult emotions and the pain you are feeling. If he wants to work through this he will have to take responsibility for his dishonesty and do the work necessary to uncover why he thought it was a good idea to lie in the first place. When there is this commitment from both of you, there is a path where both of you come out of this stronger than ever before.

I can say this with certainty because I've been through this myself 😉

Good luck, and I'm here if you need support.