Relationship... Misplaced jealously, over-reacting, I cannot stop. Advice?

My boyfriend of almost a year has a best friend, who happens to be my manager. My boss used to be interested in my boyfriend in a romantic way, long before I came into the picture. My boyfriend did not return those feelings because he is not gay. Anyway, the best friend of his is SUPER jealous of me and in return has started treating me poorly. Like so bad that I have gone home from work bawling my eyes out. I have gone to HR, and asked to be transferred to a different department (this is a work in progress of moving me). My boyfriend feels bad, and has tried to fix the situation but it just is getting worse.Now every single time his phone buzzes with his buddy texting him or asking to hang out, it stings my heart. I cannot ask my boyfriend to ditch his best friend for three years, but I cannot seem to just be content with the fact he is hanging out with a man who is awful to me. I do not claim to be innocent, I am sure I have been mean right back to my manager but still, I just want my boyfriend to put me first. What do I do? I do not want him to have to give up his friend or cut him out because of me. None the less, I am over-reacting and trying my hardest not to be "that" girlfriend. Help?