She sounds like a beastie. I'd say the trainer is right; she's jealous of you and the attention your boy friend is giving you.
I think you being the only one to give her anything is a good idea. He should only play with her when you are around, so she associates his attention, with you being there. Otherwise, she'll think that when you aren't around, she gets all his attention.
If she has a Kong toy, try stuffing it with Peanut Butter, and holding if for her while she licks it. She needs to realize that the good things come from you.
Keep at it, she'll come around! Good luck!