I am so confused, please provide advice?

PLEASE HELP!

I started dating my gf 2.5 years ago. We met at work, I was at the end of my divorce and she was then in a relationship for over 3 years. She had an emotional affair on her bf with me for 4 months before she finally broke up with him and dated me within days after.

Since we started dating, her mom has not approved of me from day 1 and this has been a complete nightmare. She has been rude to me, insulted my religious beliefs, insulted my height (I'm 5'7), accused me of blinding her daughter with $, accused me of not making enough $ (I know, redundant), has kept in contact with my gf's ex still today (she texts him, invites him over), tells the small town they grew up in how terrible of a person i am, has had 2 Private Investigators out on me (which has been verified), has called my place of employment to find out more about my position at the company, and the list goes on and on for years.

Mind you, Ive worked as mechanical engineer manager thus far in my career and have lived on my own since 17. I have never cheated, raised my hand or abused my gf in anyway and no matter what situation we go through I strive to treat her the best I can.

Her mom is 50 years old, has been married multiple times, lives off of alimony and can't keep a man in her life. She lives in a very female dominant family and there are very few guys in the family ever around. Which made me wonder early on if thats why she didnt accept me. She's extremely controlling and needs to know every detail in my gfs life even tho they live together; she emails her at work and texts her needing to know where she goes, what her plans are days/weeks in advance, constantly wants to hang out with my gf's friends, they even share a joint checking account and she monitors my gfs spending. My gf is 28 yrs old.

I am absolutely in love with my gf and adore her. However, my gf is very passive and throughout these years she doesn't stand up for me "to keep the peace" between her mom and I. She believes that keeping us separated is what's best. I bite my tongue when I'm insulted in person by her mom, I don't bring up what she's done to me out of respect for my gf and always try to charm and kill with kindness. Im always there for her mom whether its helping her around the house or any other favor. No lie, she once sh** her pants after working out and I helped her into the shower and cleaned up the mess while my gf was out. I know! Am I crazy for staying!?

My gf and i often argue over this; its been 2.5 years, we talk marriage and kids but she won't tell her mom any of this because her mom doesn't like me. My gf rarely stands up for me or takes my side and she wants me to just go with it BC "that's her family." I'm exhausted and feel like a fool.. Can you PLEASE provide some advice. thank you!