Sorry in advance for the longish post here but hear me out 
I'm 24 have a son who's 3. I'm separated from his father . We parted on awful terms but are coming ok again for the sake of our son. Will never be together again btw. But anyway. When my son was born for a year or so I couldn't face him after what had happened so I got my mother to do contact with him until i came to terms with everything my head was a mess but thankfully things are good now so it was handier for my mother to have the communication with my child's father. For this year or so anyway they got along well talked and communitcated well for the sake of my son . But within this time my mother has gotten "obsessed" or something by him🫤 my mother is 52 and my son's father is 23... when I got my own health and well being sorted me and my child's father back in December started communication instead of my mother doing it. We get along well now which is better than what we did.. so when I took over the contact my mother couldn't cope with this and started getting nasty... my child's father told me in January he had a new girlfriend and was expecting another child. As it's not my business I was ok with this and as long as it's not affecting my child i don't care. The time he has with my child stays the same and the arrangements so I said that's fine I'm not bothered. On the other hand my mother couldn't cope with this for some reason threatened to send anonymous letters to the my child's fathers girlfriend saying about the wrong he had done in the past (4 years ago nearly) I said that is completely not your business , when I told her NO it's not our business she fell out with me and said I depise him he doesn't deserve to have a life at all... he takes my son every second week so on the weekends he doesn't have him obviously being a young lad at 23 he goes out and has a few drinks with his friends (again his own business ) on the weekends he doesn't have my son the next morning my mother without fail says to me was he out last night where was he what was he doing. On Sunday I said to her why are you soo bothered like seriously! She said it's not that I'm bothered he just doesn't deserve to have a life. She said she wants him to suffer because he's out enjoying himself. All this has started since I took over contact and since my child's father has started going out and enjoying himself and has got a girlfriend. Why on earth would my mother be acting like this? It's dragging me down big time I'm starting to think am I the one being unreasonable!! It's almost as if she's a woman scorned as people would say for no apparent reason. How would I even address this whole situation . Sorry again for long post!