Depression, anxiety, anger, shame and fear are all kerosene to the flames of these feelings, and being raised to constantly assess others and judge your own worth by this same external (and often cracked and inaccurate) yardstick can lead to this as well.
But you can attack these thoughts by developing a deeper understanding of them or using cognitive-behavioral techniques to rob them of their power over you. How much is this affecting you, and how much are you willing to work at it? If you’re serious, consider those closed doors I mentioned.
Try one last talk with your ex and ask what he thinks you can do. Write her a note? Have him convey that he’d talked to you and that you wanted her to know how much she means to you? Talk with her on the phone briefly? Explain to him what it might mean to his mother as well – and cross your fingers.