Op, it's very normal and very okay to grieve your relationship. 3 years is a long time for some people. Don't expect it to be something you get over with in a week. It could take months, however do not let that leave you stagnant. Get closer with family and friends, keep socializing, get into a hobby or a job that can keep you occupied. This is just a hurdle.
First, girl I am so so so sorry this happened to you. I had a similar experience of getting totally ghosted after a year and honestly what helped was going to the gym and walking in parks. I was so emotionally distraught I was having an awful time sleeping and spending the time working out or walking in the park gave my mind something to focus on besides the despair. Also reach out to your friends, don’t let yourself drown in self isolation and you’ll be okay