I applaud you two for proceeding so slowly, and for all your honesty.
Your husband has similarities to my ex. Even though were lived mono, I was poly at heart. (This is all long ago, we met in 1974... I always just thought I was a terrible slut, until I read Opening Up in 1999.)
He had low self esteem and thought he'd married up as well. He was extremely jealous and got pissed off if I so much as talked to another man. Never mind flirted, which by my nature I did now and then, mildly. I never cheated.
However, finally, we rather rushed into opening up, had some good talks, he thought he'd like some new pussy, and like noobie idiots, went unicorn hunting. Found one, she was into him, not me, I vetoed after a few months of not being able to stand their overwhelming feelings for each other, then he resented me for having done that.
Finally we split, but for many reasons, not really over intimacy with others.
Anyway, that is my cautionary tale. At least your h must feel his cock is big enough, if he's more worried about his car and his "looks" not being good enough for ya! My ex was good looking enough and his cock and bedroom skills were terrific (he knew this), but he feared abandonment and being alone I guess... every male on earth was competition to him. He'd have kept me in a cage if I wasn't so assertive and confident!
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
Mags (poly, F, 61) loving miss pixi (poly, F, 39) since January 2009, living together since 2013
"Master," (mono, 34), miss pixi's Dom for 2 years