Sorry we haven't gotten together. I've been so busy.
And that is why we haven't gotten together.
But I know what you're thinking.
"Well, I'm busy too!"
(Because everyone thinks they're terribly busy, and work terribly hard. Except the people who take pride in avoiding work—and they take a quiet pride in how hard they work at that.)
I'm sorry we haven't gotten together.
I hope we find time to get together soon.
And leave it at that.