Anabo,
You are beta to her. She established dominance. It is now too late.
The girls who do not know you give you alpha credit because of muscles or whatever, hence they suck your cock.
Your girlfriend sees the real you, and it is not the dominant strong man of her dreams. Being submissive and pleasuring you does not excite her anymore.
My advice : find a new girlfriend and act like an asshole to her.
You friend,
RRR