Welcome to the forums. I'm happy that you've begun to be introspective about things, and I'm very glad you've made the decision to work on being more open and honest. That's something I strive for every day. It really does improve relationships, and it's pretty much essential in polyamory.
Kudos to you for recognizing the impropriety of your extra-marital relationship. That's a big first step towards openness and honesty. Anyone who's ever been affected by an affair will tell you the emotional infidelity is as bad, and usually worse, than any physical affair. You're sharing intimate feelings with someone other than your spouse, and to a spouse this can be devastating.
It apparently was a shock to your husband's system when you mentioned the idea of poly. Question: Did you mention it as a thing you would like to do in general, or did you mention your affair partner specifically? There's a big difference in how most men are going to react to those two questions. In the second instance they are likely to become very territorial and not likely to be able to discuss the situation rationally because of the raging hormones that hundreds of thousands of years of evolution have established in us when we feel competition.
I'm sorry you're feeling the loss of your partner. But I think you did the right thing by stopping that, realizing the unethical nature of it, and beginning to concentrate on your husband. With time, and with the strengthening of your bond with him (which is something that will serve you well should you later expand your life to include others), you may gradually and slowly introduce the idea to him. There are a lot of wonderful threads about introducing poly to a spouse. Read these and learn from others. Plus, other, more experienced poly folk will be along shortly to give you some wonderful insights.