Many past losses, suddenly grieving

In June of 2015 my best friend’s fiancée died suddenly and unexpectedly four weeks before their wedding. It was very difficult to cope with, especially because my friend’s daughters were 7yo at the time. In the following six months I lost five more people. None of them were as close as my friend’s fiancée, but all but one were sudden and unexpected and it felt like a fresh wound every time. I also lost two beloved pets in those six months. I didn’t know how to deal with those losses because I didn’t feel like I was grieving so much as grappling with the concept of death in general. For a long time I was worried about others dying. If someone was a few minutes late to something I would worry that they had died even though I knew it wasn’t a rational fear. That response has mostly faded by now.
Then in February last year my best friend from childhood through young adulthood passed away. She had stopped talking to me a few years prior and I was still somewhat angry with her, and I didn’t know how to grieve someone that I had already lost. I wasn’t sure that I even needed to grieve for her, and so life went on. Back when we were in our early 20s we made a pact that if neither of us had children or prospective co-parents by the time we were 35 then we would raise a child together. Two days ago would have been her 35th birthday and mine is in two weeks. It has hit me really hard.
I don’t know if what I’m feeling is the compounded grief of all of the losses I never dealt with, grieving over my friend who I never got to say goodbye to, sadness over my lack of children, or if I’m just fragile because of another friend’s attempted suicide last week. Perhaps a bit of all of the above. I do think I need to do some work grieving for my friend, but I also don’t know how to do that when she’s been gone for so long and I still feel angry at her.