I am glad you could get it aired out. I am sorry you feel upset. It is not fun to feel.
Since the change point in your feelings seems to be her moving in with him... let me throw out some possibles.
Could it be you are experiencing DISPLACEMENT? Could you have wanted more check in - collaborate from him before
he invited her to live with him? Especially since you were all planning to move in together and you wanted to slow it down because learning to deal with bipolar was leaving you feeling unsettled?
Could it be you are experiencing ENVY? That now she has what you wanted? Living with him?
What do you need from
to feel at peace? Could anything here help you articulate how you are feeling?