If he always has to seek his mother’s advice when it comes to the handling of your relationship, it is time to hit the road.
If his mother is constantly finding fault with you, with no probable cause, then your relationship with her son is doomed.
If his mom insists on accompanying you and her son on trips or events, she will eternally be a thorn in your side.
If she blames you for everything that goes wrong in the relationship, run, do not walk.
Finally, yet importantly, if he is an only child, need I say more?