I'm a bit late, but here's my story.
I met him --let's call him "Josh"-- when I was in high school. At first, he was a little off, but not too weird. I liked him because we were both vegetarians (we originally bonded over this fact) and sort of the hippie type. We were both super into the same type of music and generally he was pretty chill. However, the rest of his friends, none of who I would dare be seen with in public, were complete creeps. That should have tipped me off. He lived very close to me, so he ended up driving me to and from school almost every day.
Things escalated very quickly. It wasn't uncommon that Josh would bring be breakfast every morning-- I'd guess he spent about $6 every day for a few months buying me something nice to eat. I would tell him daily that he didn't need to do that, especially since I told him very firmly I would never be able to pay him back, as I was always broke. Eventually one day, I got sort of angry and really put it in place that isn't inappropriate for him to be doing this for me. He also carried a couch from his house (about 1.5 miles away) to my apartment after I said it looked cool, and he decided that I must want it in my living room. I wasn't even there when he showed up at my house with it. My father was like, "Who the fuck is this guy at my door with a couch?".
Anyway, he kept trying to pry into my life in weird ways, such as bringing me random expensive and very personal presents. After Josh and I met, I ended up with a boyfriend (who I was later engaged to and ended up marrying very shortly after I graduated high school). He knew about him and even met him multiple times.
I found out about a year after I graduated that Josh had been telling everyone at school and who he worked with that we had been dating during our entire senior year of high school (keep in mind he knew about my boyfriend/engagement). I used to keep in touch with him, but I haven't spoken with him since I heard about that.
After that experience, I make sure to listen when other people tell me they get a bad vibe about someone. I guess I should have trusted my friends' instincts.