You mentioned that it feels like someone dying. That's because what's happening is you are in a grieving process over the loss of someone you love. Grief isn't necessarily predicated on just death. Grief can be experienced over most any type of loss. Whether your relationship ever took off or not, you had a dream of a great relationship with this person that has not come about. What's happening now is that you're grieving over the loss of that dream.
There are stages to grief - anger, denial, bargain, depression, and acceptance. They don't necessarily occur in that order and some of the stages may even repeat until you're finally able to reach acceptance.
Once you understand that what you are dealing with is grief, you will have a much better go of it because you will have an understanding and can at least recognize why you're going through those feelings.
Hope this helps! 
