My mother is causing problems in my marriage?

"i am from kenya. my husband and i are not legally married, we had planned to get married but on the day of the ceremony his ex baby mama showed up and objected to our union, that was in march last year. till today we haven't been able to legalize our union because his ex's letter of objection is preventing this and she refuses to let it go, i cannot explain how this makes me feel and every time i think about it i cry. from the moment he and i became an item my mom was aware of everything that we went through, our struggles and our hardships and she kept encouraging to stay strong and stick together so we decided to move on with our lives as a married couple, we have a 7month old son. initially my husband and i were living in the same house as my mom and at some point he felt uncomfortable and that it was disrespectful to my mom to live in the same house as him so he opted to move out and asked me to go with him, my mom didn't take this well at all because she felt like i was abandoning her and at some point they got into a heated argument and he threatened that if i didn't go with him he and i would be over. so after talking to my mom she let me go and said she is ok and very supportive of our relationship but my husband doesn't feel that way because every time she wants to see her grandson she waits till he leaves the house and even when she wants to pick him up she asks the nanny to meet her out by the road when he's home rather than come in and pick him up. my husband feels like she doesn't want us to be together and it's starting to affect us, he doesn't want our son going to her house anymore and even though she loves her grandson so much it's like she doesn't recognize that this man is the man i have chosen to spend the rest of my life with and that he is the father of my son, even after watching us go through such a hard time.when i ask her about why she does these things she says that he is picking on her and that she doesn't do this at all. My husband says i defend her too much but all i do is explain to him exactly what she tells me. i have spoken to her over and over about this but it's like she doesn't hear what i'm saying. i feel so torn up and stressed about this and i know it's only a matter of time before i go into depression because i have so much i am trying to balance in my life, being a mother and providing for my son, trying to feed and support my mother who relies on me, trying to concentrate on my job but mostly trying to be a good wife to this man, also there are many times i think about whether he communicates or sees his ex and if there's something going on, our sex life is not what it used to be ever since i had the baby and it's also affecting us, all these things combined are slowly eating into my energy and again it's only a short matter of time before i go into depression, i can feel it and i don't know what to do, these are 2 people who matter so much to me and i don't want to hurt either one of them, sometimes i just feel like taking my son and leaving everything and everyone behind and start my life fresh, i love my husband very much, i love my mom very much too and i would be so happy if all this nonsense between them could stop. i'm so exhausted and stressed out by all of this, what should i do?