What should I do if my boyfriend doesn't want kids but I do?

My boyfriend and I have been together for about a year now and recently we have been talking about kids. We are not ready to have them now but eventually I wanted to, however he doesn't want to have kids anymore because he thinks that kids ruin the relationship instead of bringing it together. He wanted kids in the beginning of our relationship and now he doesn't. He also has two other kids from a previous marriage and I feel like he can have children with them, but not me and it really upsets me. He also has been talking about getting a vasectomy. I don't kno wat to do can anyone help?