Most Helpful Guy
In a couple people discuss things that consider the couple. Vasectomy is definitely one of these. If he went behind your back there's not much room for anything else then 'moving on with life'. It's his choice not to want more kids, that's fine by itself, what's not fine is that he made that decision without letting you know beforehand. If having kids is something important for you, and he does not want them with you you should stop wasting time and energy with him. Don't go for half-half solutions like staying with him and go for a sperm donor, seems to be a pandora's box of weird feelings, also for him.
Move on. Make sure you discuss early in the relationship about your childwish and make sure that your next partner is not too afraid of that. No need to jump the gun, but just to make sure that he's in it for the long run, at 25 you still have some leeway.
Most Helpful Girl
If you want to be with him long term and having kids is a deal breaker for you then I believe you should leave him. In the end a strong desire to have kids when you can't will only lead to resentment in the long term.
Is there any reason he went ahead without telling you?