I hadn't seen my ex for a year before last Friday. He came to my place of business, and was nice, although he used the "F" word in his opening sentence to me, while complaining about my coworkers.
He had to come back this past Monday, and was his usual downer self.
I am TOTALLY okay with this, because at this point, I realize he is just being himself. I don't not have any expectations for him, and I do not look to him for comfort or validation.
As a matter of fact, I don't look to ANYBODY for comfort or validation at this point. Friends who will do this for you and are real, are very rare. I have some new acquaintances who might or might not turn into real friends. We'll see.
If you are okay seeing your ex without getting upset, then so be it. It sounds like this is difficult for you. All you can do, is what you can do.