Cassielove, again, your problem is extremely simple. Everything stems from one main issue and that is your deception about the birth control. I strongly support you in your decision to stay on them. Parenting a child means at times their needs are placed above your own. You have shown epic fail in that regard so far. Keep the pills handy,,,,always!
You are hearing what you want to hear from your husband. Remember, he is basing everything at this point on your original lie. Be honest with yourself first. You really are the one wanting to be with others. You are hearing from your husband only the parts you agree with and want. Your husband mentioned sharing you with three men so the father wouldn't be known. Father being the keyword here a.k.a you pregnant. Has he ever mentioned sharing you without the pregnancy part? Would he even be considering this if he knew you were still on birth control and merely looking to cheat?
Your husband is already beginning to suffer esteem issues from your lies. If he is, even in fantasy, considering a baby with you come from another man, then he is starting to doubt his ability to get you pregnant. Have you considered what may be going on in his head from all this. You mention you know he is frustrated. Are you aware of any of his other feelings? Is this your goal? Do you wish to continue deceiving him to the point he stops bothering in trying to impregnate you, or do you want to take it all the way to completely crushing him as a man? I feel sorry for your husband. I really do. He loves you and trusts you. What a complete fool.
Cuckoldry is great when there is honesty, communication, and when both the husband and wife have agreed going in. But to fuck up another human being through lies and deception just so you can play out your desire to be the company slut is wrong.