Hi, I'd like to help you with your question.
I understand your feelings about your ex. It sounds like you feel very strongly about being with her and that you still have feelings for her. You have made attempts to stay in contact with her and keep some level of relationship going with her. Yet she continues to keep you at a distance.
It may very well be that her depression affects her. Lack of motivation is a big factor in depression. The person feels the feelings, but is not motivated to follow through because they don't have the energy.
It also could be because your ex has personality issues. Some people, along with being depressed, may have dependent personalities. This causes them to have difficulty with making decisions on their own, and this would affect her particularly if someone (like her son) is telling her what to do.
If you feel that a relationship with your ex is the best way for you to go, then continue contact with her. She may not respond the way you wish, but this may have to be the way it is for a while until her depression gets better, or she makes a choice on her own. You can give it a period of time to see if things improve by then and make a decision from there.
Also, it may help you to get counseling to sort through your feelings and be sure you are ok with your relationship the way it is.
I hope this helps you,