You're doing just fine. Your girlfriend's mom is a cow so don't let her get to you. Is this who you want for the grandmother to your children? Just sayin'...
How are you hearing all these bad things about yourself? Is gf's mom telling you to your face or is gf filling you in? If GF is passing along her mom's B.S., then I'd reconsider dating her. She is also a rude cow with no common sense or concern for anyone else's feelings.
In a healthy, functional, mature situation, it's not an issue if one's gf's mother doesn't like them as long as she is polite. If she isn't polite, your gf needs to tell her to shape up or cut her out.
Life is full of people who don't like each other, especially in-laws. It's no big deal as long as everyone behaves themselves. But if gf's mom is going to hurt you over and over and gf doesn't do anything about it, this is a toxic situation and I'd recommend leaving.
I'll bet in the navy you learned some self-discipline and professionalism. It doesn't sound like the women in your life have.