I think in this context "I don't buy it" is closer to "I think you are misinterpreting your feelings" rather than invalidation. I agree - it's more about her s

I think in this context "I don't buy it" is closer to "I think you are misinterpreting your feelings" rather than invalidation. I agree - it's more about her saying something like: "I'm not going to take your apparent desire for a divorce as 100%, literally true (yet) because I know you've got a lot of emotional 'stuff' going on right now. Go and do your thing, take some space to work things out, and if you do work it out, come back and let's talk again. If you're serious, we'll figure that out at the appropriate time." which is a very mature reaction, in a way that invalidation wouldn't be.