Will the negativity ever end?

So to try and make a long story short my SO has a five year old son with an ex that he gave his rights away too and allowed his best friend to adopt him. He had violated a term in his probation and ended up in jail, while in jail his ex got together with his best friend. When he got out he wasn't in a good spot financially or mentally to be caring for a child. Despite the kick to the gut to see his best friend with his ex, he also knew he could give his child the life he deserved where as he was unable to do. So his ex and best friend married and have two other children of their own.

My SO and I have a two year old and 5 month old. He has made strides in his life, he works 60 hours a week, hes a loving dad and supporting partner.

Now this is where the negativity takes place. If I ever see his ex in the store she gives me the most awful death glares. She has mistaken my mother for me as we look a lot alike and she just mean mugs and goes out of her way to not be near us.

When I first became pregnant 3 years ago, my SO and I had broken up and she was the first person to reach out and offered me a lot of help and support if needed and made the comment "our kids are half siblings after all."

But as soon as we got back together all communication ceased and shes been bitter ever since.

I'm just confused because first of all, we are adults and should be a little more mature than that. And secondly shes married and has two other children and is completely moved on (at least physically)

I'm not sure how to reason her actions or if I just need to ignore entirely. I wish things could have been different. My SO has reached out a couple times to his old friend and thanked him for stepping up to the plate and being a good dad for his son. But its always a dead end conversation. Hes only reached out twice so he wouldn't be like harassing him or anything.

One conversation they did have my SO asked him why he hates him so much and his friend told him he doesnt hate him but his wife does and she wouldn't be happy if they were communicating.

It's just all mind boggling to me and she must be tired carrying around so much anger and resentment

@Nel I'm not looking for her to smile at me and be all buddy buddy. But its pretty uncomfortable walking into a store and being stared down as if I had just killed her dog. I'd rather be ignored than have this cloud of negative energy radiating off of her towards me 🤷🏻‍♀️