My only boyfriend in high school was obsessive like that. I couldn't talk to any of my friends, had to stay on the phone with him til midnight or later every night, spend each weekend with him etc. It was pretty bad. Of course when my parents set boundaries, because he'd tell me I "wasn't allowed to" do whatever, he'd throw tantrums. He'd refuse to obey my parents' curfews, until he was no longer allowed at my house. After about 8 months of this I became super distant and he got more clingy. When I broke up with him (on my 17th birthday, no less) he just didn't accept it. It was baffling. I had to tell him three times that we were no longer a thing before he finally accepted I was serious, and began spam calling me each day for months. By then he was a freshman in college and I a junior in high school. One week I had around 300 missed calls, 50 or so in one day alone. My parents had to take my phone away from me for quite a while.
When I saw him five years later, he said he'd never gotten over me, and went as far as buying a gun to commit homicide-suicide because he didn't want anyone else to have me. Even moving and changing my number and everything didn't help calm my stress and paranoia until quite a few years later.
People can be deranged.