Welcome to the forum.
What the others have said is true, honesty needs to be 100%, and you need to sit down with your husband (with a poly-friendly counselor if possible), to figure out if your marriage with him can be re-worked/resolved in a way that works for both of you.
Also, have a caution about this "other guy from your past." He seems to have a habit of periodically changing partners. You could be giving up your marriage to your husband, only to get a temporary relationship in return.
Really I think you should take some serious quiet time by yourself and just think. "What is it that I really want? How can that goal be met? Is there a way to go about that with the least possible harm to the least number of people?
Tell your husband you feel suffocated. He has to know. Have some long heart-to-hearts with him before giving up on the marriage. And like I said, be aware of what you will have when the marriage has been dissolved. Will you have the life you want? If not, what would you need to do to get that? and as always, things need to be done so the least possible number of people suffer the smallest amount of hurt.
Don't rush anything right now. Give yourself some time to think.
I hope we can be of some help.
Love means never having to say, "Put down that meat cleaver!"