I want a baby but my husband doesnt,how do i get over this?

i have 2 kids my husband have 2 kids but there much older then mine, when i met my husband i told him i wanted 1 more baby, (he had a vasectomy years b4 we met) i don't see my kids much and it hurts because i don't feel like a mom anymore because i don't have my kids and his kids don't look at me as a mother figure, it hurts so much and is a sensitive subject for me, he did tell me yes having another would be great, but now for the last 6 or month months hes only worried about buying his kids a car and paying for his kids college and doesn't look at my pain that I want one more baby, this is pain full for me so how do i get over the possibility that he wont get a reversal and give me the one thing that i want to be part of both of us?