So how do I (a) forgive my husband for not wanting a third, because I can’t help but feel angry at him, and (b) accept that it’s not going to happen – when I just don’t want to give up the dream that someday I’ll be snuggling a newborn again?
Because to keep indulging your desires over reality will, if not already then soon, make you a bad spouse and a bad parent. Your husband needs you to respect his limits; he’s already met you at a darn good definition of halfway, since you now have more children than he wanted and fewer than you wanted. What more do you want from him – transformation into somebody else?
Your kids, meanwhile, take their emotional cues from you and your husband, so they need you both to model maturity, healthy choices, mutual respect, and a freely chosen commitment to the collective good of your family over individual preferences that, if acted upon, would damage the whole.
I do sympathize; a baby is less of a want than an ache. It is understandable, too, that letting go of the baby idea will come with reluctance and a wave of grief.
You just don’t have the luxury of taking this depth of feeling as license to go wherever those feelings take you. Cry, stomp, whine to your friends, acquire a therapist just for this purpose, yes, then let it go.
As for how to “forgive” your husband, I suggest following his lead. He’s still by your side, right, after not one but two “oops” pregnancies? Either you’re singularly bad at managing birth control, or he has grounds to point out the cloud of suspicion under which you lately reside (and either way you’re overdue to discuss his getting a vasectomy). You both have let each other down – as spouses inevitably do. Neither of you can provide everything the other needs.
When you are ready to accept this, chances are there are newborns who badly need snuggling in a hospital near you. The right volunteer opportunity could match your need with a vulnerable someone else’s – with nothing for anyone to oppose.