That's definitely unfortunate.

However, if you are at the point that you are going to end the relationship anyway...

Have you tried direct communication with them instead of speculating on what's going on? Have you ever said to them straight out, I feel like you have become more distant with us this year and I'd like to understand why. Can you tell us what is going on?

I'm a big believer in direct communication and shining a spotlight on poor behavior. It is much harder to make the snide comments, etc. when people are called out for it in a polite but firm way. But you also need to be prepared to listen to what they have to say and sometimes that means hearing some truths about ourselves that we don't like hearing.

But in the end, if you have tried improving the relationship and it hasn't worked out, then yes, cut your losses and move on.