What does that mean, that after 3 months it was too late? Have you two had discussions since that time, and what reason does he give for not wanting more children?
I, too, find it strange how he vehemently doesn't want children, yet he uses the risky pull-out method. You shouldn't even risk becoming pregnant right now because the marriage isn't stable. No sex for years. Now, your extreme emotions about how it's performed. Children should only be born into healthy relationships, if it's not a single person choosing to have a child with a donor, etc.
I have known of some women who are so overly focused on the children that they neglect their spouse. They seem to value mother/child relationships more, and avoid everything or many things that should be shared with a husband in a healthy marriage. Really look at yourself and decide if this is the case, and that with your other children growing older, that you just want another one so you can continue devoting your time and energy on them which lessens the time and energy you have to spend on your spouse.
It'd be one thing if you married and he changed his mind about having any children. But that didn't happen, and even if he initially wanted 3 or more, he's in his rights to change his mind, just as if the tables were turned and he wanted more but you didn't. Would you want him to be refraining from sex for years and have a lot of emotional strife that he wasn't seeking therapy for?
I know that when I married, I initially wanted 4 children, but changed my mind early on to have two. Sometimes you have to experience the reality of life with children to see how things are, and it's realistic to expect one might change their mind about the number of children originally planned.
You have to try for emotional maturity and respect the wishes of a partner, if he is reasonable, which your husband is. If you can't manage emotions like this on your own, it's up to you to do the right thing and seek therapy. Take care.