Without knowing your husband’s reasons for not wanting more children, I cannot presume to say whether or not he has just cause for his desire. What I can tell you is that for just reason a couple may choose not to have more children, presuming they do not use artificial contraception or sterilization to render their marital relations infertile.
I suggest that you and your husband talk about your desires and your reasons for them: your desire and reasons for another child; his desire and reasons for not wanting another one. If the two of you need help in discerning whether or not you have just cause to stop seeking to have children, I suggest talking with a balanced and orthodox confessor or spiritual director. You may also get a referral to a Catholic-friendly marriage therapist in your area from these sources:
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