i (f) have had a crush on this guy on and off for over a year now, we used to be roommates but now we are just co-workers. i find myself thinking about him almost constantly and i get very possessive when he talks to other people on the phone or goes out to lunch without me, even though i keep telling myself to leave him alone and just be friends. 

he is the only friend i have and he's nice to me and single, but i am scared that i have an obsession with him...is that a part of BPD for anyone else or am i just being paranoid? i've never been in a relationship or had sex so i can't tell if this is normal thinking or not. do i have hormonal issues or is the possessiveness is from having BPD?

(my obsessiveness might be because i am trying to *not* have a crush on him, he is a family member related by marriage to my sister and if anything were to happen it would probably end badly...and he's 7 years older than me.)