Yes, my XAH very much affected my job performance, which wasn't really good since I'd *just* been hired here when things started to get hairy. He started dropping in to meet my bosses (i.e. "check up on me" and assert his ownership of me). He would call me several times a day and email even more. When we separated, he started harassing me and yelling into the phone. I was afraid to pick up the phone, which isn't very productive if you're a secretary.
When things really started to unravel, I went to HR. I told them what was happening so that it was clear. They worked with me but I wanted to make sure that I didn't acquire a reputation as a "problem employee" so I treaded carefully. I was given a phone with caller ID when the rest of the firm didn't have them yet. I was offered a few days off, unpaid of course, to deal with things like going to court or medical appointments. I used all my sick and personal days without guilt, knowing I really needed them then. I spoke with my boss and told him about XAH's threats to go after him directly; he took note of the situation and assured me that only idiots go after partners in a giant law firm, and that he would take steps should XAH bother him.