I don’t want kids

I don’t want kids. I don’t want to give birth and go through pregnancy. I however would be willing to adopt, but way in the future. We don’t want kids now, but we’re scared this is gonna be a problem if we pursue a relationship any further. We have been together for about 4 years and in the past I thought I wanted kids, but I realised that I only felt an obligation as a woman, not actually wanting it.

I feel like a failure, and I feel so guilty that I don’t want kids. I know I could change my mind in the future, and that scares me even more. I know he wants to have children with me someday, and I wish I knew sooner I feel so bad for him and it’s hurting me so much that I don’t want to go through pregnancy or birth. I don’t know what to do, we’re taking a minute to think about everything but I can’t get past this sense of failure and disappointment.

Maybe once I have kids the feeling will kick in? I’m so scared and hurt from myself, does anyone have any advise or wise words to share please?

Edit: I’m 18 and he is 21. I know we are young, but we are together and I want to prepare for the future in the case I don’t ever want kids...