Re: My best m8 loves him.
Your issue here isn't with your boyfriend, it's with your girlfriend. She's not very loyal (to you or her current boyfriend), and frankly, I think you need to 'throw her under the bus' (which is Yank-speak for 'dump her'). No real friend ever contemplates stealing their friends boyfriend. It's selfish and self centered. And frankly inexcusable.
There's no issue with your b/f, he's done nothing wrong, and there's nothing wrong with someone else liking him. Until he does something that indicates he's taken your 'friends' bait, I'd leave it alone.
Tell her to take a hike, however.