Unfaithful Lover

I feel that this is where your energy should be going – rather than wasting too much of it worrying about how truthful your lover was.
One might look at it this way: you were married. From that point of view you were not in a position to be utterly faithful to your lover because you also had a husband.
Maybe your lover felt that it was perfectly 'fair' in that case to have someone else himself. I don't know.
People justify their actions in strange ways. And I doubt if you will ever reach into his brain and find a complete answer to this.

So, what can you do?
Well, is it going to help to have some sort of contact with this lover and to try to find out what his reasoning was? I doubt it.
You're trying to rebuild your marriage and I'm not sure how your husband would feel if he knew you were in touch with the other man – even if it didn't involve romance or sex.

But what do you need to do to put this behind you?
Well, people often find it helpful to write a letter - pouring out everything they feel – but then not sending it. Sometimes they burn it in the garden.

This signifies the end of the matter.
Another thing you might do is to have a couple of sessions – on your own – with a counsellor at Relate.
If you could talk over why the affair happened and whether or not you were ill-used and what that means, then you might feel more able to put the past behind you.
Personally I think a lot of your feelings are really about guilt that you could have hurt your husband and family.
So maybe you are channeling this guilt into feelings of hurt and disgust at your lover.
But the sad thing is that it takes two to have an affair. You are both adults. It has happened – but it's in the past.
Your future now is with your husband and I feel you must do everything possible to prove to him that you are wholeheartedly devoted to the marriage. Settling old scores with your ex-lover is not likely to help, I fear.
I know you haven't been dumped exactly, but some of the advice in the piece should help you to clear your mind of the past and to move forwards.