After 2.5 years and planning a future together, bf decided he thinks he wants kids

The classic tale finally happened to me. I've brought up multiple times that I don't plan on having kids (started dating at 24y.o.) specifically because I didn't want this to happen, last time we talked about it he said that life with me was enough and he wanted to marry me. Of course once I got on board and we started planning on moving in together, he decided that actually he does want kids. Obviously I'm devastated. I'm of the personal opinion that men who want kids have no real concept of how hard it is, and he couldn't say why he wants kids besides the general "needing a legacy" idea. So I told him he needs to do some real research and soul searching. Because I'll be damned if we have to give up on the best relationship either of us have ever had over an uninformed decision and vague vibes. I know we'll probably have to break up. So I'm getting myself back in therapy and refocusing on my friendships and working on my budget to be able to adopt a dog soon. And crying. A lot.