Disagree on getting tubes tied.. Any advice?

I'm 26. I have two kids already. I want my tubes tied, not that I would mind having another child but because of a cervical cancer issue it's basically now or never. SO doesn't want a baby now, though he's been promising we can start trying since before Christmas. Problem is, I can't wait any longer because I need surgery on my cervix, after that I more than likely won't be able to carry full term which has always been an issue because of my uterus anyway. I'm not in any position to lose a baby at 6 months. So I don't want to chance it. I've decided to get my tubes tied because I'm just not a BC person. And I'm tired of tracking fertility for no reason. Now since September I've been telling SO if we aren't going to try, I'm getting them tied. So it's that time and I called the doctor. He says that's not happening and I'm not doing that. But I feel like I've given him the chance and he let that pass. He knows the issues and have since we met. I'm not sure if I should just do it anyway and let him know I am or just not really mention it again and do it. Any advice?