tl;dr I think my ex was banging a highschool girl with Tourette's while I was at work
Several years ago I was living with an ex who I had met working as a cook. We were together for a few years. In that time I went on to work in another field with better pay and benefits and he kept working in quirky little bistros and coffee shops where he made barely more than minimum wage.
This eventually became a bone of contention as he could have gone just about anywhere and made more, combined with him not giving me enough for his share of expenses and then saying it was because his hours had been cut. He told me for months that he was looking for other jobs and was still working, I found out later that his resume wasn't even finished and he was coming home right after I left for work in the morning.
For several months he lost interest in me and would avoid any and all attempts to initiate sex. I eventually found a huge browser history cache of spankwire videos all having something to do with "18" "19" and "barely legal" on my laptop (he didn't have his own). I wouldn't have had a problem with the porn if our sex life was normal and what I found hadn't been so specific and exclusive of anything else. I started finding hair ties all over the house. My hair was jaw length, so they sure as hell weren't mine. I tried confronting him about these things but he always had an answer and I was becoming too exhausted by it to try anymore.
He had told me about a teenage girl who worked at the restaurant with him who had Tourette's syndrome. He talked about her and he tics really often and I thought it was just idle fascination. We went to a house party with his co-workers one night. We were sitting on the couch when she arrived, my ex waived to her, she looked at us, and immediately went from normal calm conversation into total meltdown. She starting chirping, making these jerky hiccuping sounds and motions, and was taken by other guests into another room to calm down. She stayed there until we left.
At the time I didn't really piece this together. Now it just seems a little obvious.