Hey Tessa. My H went back and forth for several months. He swore he broke it off, then I would find texts on his phone. He would deny it. Eventually I broke it off for him. I wouldn't recommend that, it's just what worked in our sitch. I literally called her and told her to stop calling, and when she kept calling, my DH changed his number and luckily (they were co-workers) her shift got changed to third shift. (Didn't have ANYthing to do with my friend that worked in their HR department, honest.:) ) Anyway, eventually, she tried paging him at work, or waiting around to see him leaving work, but he ignored her. She was hispanic, barely spoke English (he does not speak Spanish) so I had a friend who is Spanish call and leave a message on her phone. Her husband picked up her voice mail and finally, she stopped calling my husband.
After the alien returned my H, he admitted to me that he had thought she was the love of his life. They had this "token" of their love that he carried with him everywhere.
Again, after my H came back to his senses, it was really like he had woken up from a bad dream. The selfish and hurtful A-hole (really, for lack of a better description) that he had become totally disappeared, and the tender, loving, caring and honest man he had been returned. He told me then that he doesn't know what he was thinking, I was always his best friend and the love of his life.
So, yes, it can take time. Yes, it is hurtful, and yes, it can happen.
My H and I are on the boards now because of a completely separte issue, but our M is very happy for the most part. And we are almost through working out our remaining issues, which have to do with healing and moving on.