On top of all this there is your mum to deal with. You allude to a history of having a parent who for whatever reason has been unable to meet your emotional needs. It sounds too as if she is unable to meet her own needs and looks to others to do that which often ends in family members feeling crushed by the weight of being made responsible for another's happiness and wellbeing. Your mum may have BPD (I'm not qualified to diagnose) but whatever is the issue, it's been a significant feature of your family lives together. Now though, an important part of the family system is no longer there and so the family dynamic has shifted leaving you and your brother unable to contemplate contacting your mum, let alone spend time with her.