Have you ever had almost an obsession with someone?

I say almost obsession cause it's not ALWAYS in my mind...but there's this person that I don't see anymore that keeps haunting my head, I remember her from time to time and I get super emotional. Now this might seem not that weird but the thing is, I was never close to this person, we were never friends and I haven't seen her in years. The only thing is that I always found her really interesting and wanted to know her more so bad and always watched her in class in enjoyment... not seeing her now, feels like I've lost her story, it is annoyingly painful... she once approached me and I pushed her away suspecting my feelings might be love. You see, it would be a gay relationship which is a sin where I live.

So... I never truly understood what's going on. How could it be love if I was never really close to her? And I definitely don't know her anymore, after years, everybody changes. So am I just confused cause I have a hard time with emotions and recognizing them? Is it just the despair and hopelessness, the thought that I might never have a romantic life? Is it kind of like mourning? I really wish to know what's going on with me and stop my feelings, it gets really painful at times.