It just more unfinished business dear Nikki. You didn't get to say goodbye to your dad and now when anyone leaves and you find that you "get to", "have to"....it's a reminder. That emptiness will eventually get filled up and the resentment will go away. Granted you'll never be the same but trust me, you will be okay.
I used to think that our Michael died alone until I realized that God was right there by his side. When I finally came to believe that I stopped being angry and just settled for learning to accept a life without him.
It took a lot longer than I ever dreamed it would. I can do goodbyes but for years I sobbed in church...very disturbing to the Pastor but my choices were stay home or go there and sob.