OMG! You sound like a very loving mama at her whits end! It sounds like you and your little guy are going through a rough time:(
I'm a new mama of a 9 month old so don't have personal parent experience with this kind of situation but when I was a nanny the little boy I cared for did the same exact thing to his mother! It was obnoxious! I'll share what work I did with the mother and son in hopes it might help?
First, it's bullying behavior and what I I know about bullies is they are very insecure and need to control in order to not feel so out of control. The problem is, he's too young to feel safe having control and needs his parents to relieve that pressure for him. The first thing we did was to establish what he was allowed to do with him (he had to be part of the process so it could be referred to at times of consequence and reward...follow the contract as it's written and remind him when need be). This way he knew what positive things and rewards to expect for positive behavior. Then we made a very short list of things he wasn't allowed to do with him...some things only he wasn't allowed to do because he was the child and this was explained briefly...briefly! Then we listed what NO ONE was allowed to do, even parents. This was to assure him that no one is allowed to be mean or disrespectful without consequence. It was tough at first for the parents to agree to, but by having him enforce consequences for meanness it taught him why it's important to be nice. His young mind needed to experience both sides to 'get it'.
The idea is, as he ages and expectations change, he has a role to boost confidence and help him truly know what to expect if he violates the contract).
When he was mean, there was no discussion at first (because it was so frequent), just an immediate time out and loss of a privellege (game, toy, etc.). After the consequence there was a discussion about how he can manage his feelings different next time and what the parents can do to help him next time if he is unsure of what to do. He ended up asking for a time out in an area he decorated with art for when he felt he needed space before blowing up and having a consequence.
It hurts when your child says mean things to you and is difficult not to feel wounded. Just know he probably doesn't hate you so much as is unable to process his emotions adequately at such a young age...he needs your help. Don't let any form of disrespect slide by...no rolling eyes or mumblings. But don't get angry either. Express it hurts your feelings to hear because you love him but that the rules are the rules.
I also had the parents take special fun time each week to build their positive attachment. Just fun. If something happened negative during the fun time, maybe leave and tell him you'll try again tomorrow and that for awhile it was fun and can't wait to try again tomorrow.
If you have rewards and love, and consequences (discipline not punishment, because we want long lasting success), typically children respond well. The little boy I nannied for took about 2 weeks to make significant progress and within a month the parents said they were so happy to have their son back! He never left, it just felt that way because they were all stuck, especially the little boy.
Be firm, consistent, praise when earned (no praise for simple things like breathing!) And remind yourself he loves you but when he bullies you, he doesn't love himself much.
Not sure if this helps or if there are things happening that go beyond this. Just know he most likely feels safest when he knows who the parent his and when he isn't allowed outside clearly marked perameters. Maybe try to get dad on board. If dad won't go along, still have it set up to where your son has no doubts as to what to expect in your home for both rewards and consequences. His teachers and peers will thank you once he gets to age 10 for sure!
Good luck, hang tough, and when you think of it, remind yourself he only has one mama and needs her to be assertive and loving...both...not one or the other:)