Sounds like your classic case of girl best friend secretly has crush and is now hurt because she didn't say anything and he started dating somebody, or she's a crazy control freak lol

If I've said it once, I've said it a thousand times: do NOT get into a relationship with someone who has a best friend of the opposite sex. It's bad enough that he's keeping you hidden from her to spare her feelings...but to then get mad at you on top of it? Just leave now, while the relationship is still fairly new.

He’s trying to keep your relationship under wraps for her. Who the hell doesn’t update a best friend when they get into a relationship with someone else? Opposite sex or not. He obviously didn’t want her to know because he most likely has a thing for her or she has a thing for him. I would leave this relationship because you deserve someone who is proud to have you and show you off.

Run now. You deserve someone who loves You and wants to be with You and wants others to know about You. This feels like you are the side chicken in the relationship. Nope, he doesn't properly cherish You. and you deserve someone who does.

Red flag. He doesn't sound trustworthy, rational, or like he can keep his priorities straight. At best. At worst, he might have cheated on you with her, given the opportunity.

Observe the gigantic, flashing Red Flag and then dump him. He's filling in time with you before his 'true love' finally 'recognises him as her soul mate' 🤮 Run, Forest, Run!