Coping with loss of partner

My boyfriend of 4 years and I decided to go on a really long road trip. It started out okay but as more time passed I realized I was becoming depressed and in turn was struggling with the constant companionship while being bipolar. I found myself getting agitated and annoyed by every little thing he did and then began nit picking everything. Without the ability to seek a proper safe space things started to crumble. After 70 days on this trip he told me he couldn’t take it anymore and was done. He left me in a safe place in Michigan to fly back home while he would drive back without me. Im so afraid of losing him and I just want to know how to manage that awful side of this that can devastate relationships...