I've been married now to my wife for almost 2 years. She has had CFS for probably 15 years. I was just diagnosed with it a few weeks ago, but have had it now for 1.5 years. It was Mono that did it to me.
Before feeling this way, I didn't really understand her. You cannot truely know how it feels to feel helpless and envious of someone who has what you don't, until you have it.
Imagine that you're a musician. You grew up around music. You went to school for music and you're about to have your first album hit the charts big time... then, and accident. You lose your arms. You can no longer play music.
This is how we with CFS feel. Everything was great, until this happened. Now, we just watch life pass us by.
CFS can wreak havoc on a relationship because it's hard to care about others when all you can do is think about how misreable you are.
The one thing your ex needs right now, is a friend. If I didn't have my wife, I don't know where I would be.
Good luck to you!