I don't know how to live alone,
That state of being is so hard. Many, many people who go through a divorse or the death of a mate feel at sea, rudderless and lost.
I am sorry for her leaving. Are you able to figure out why she felt the need to leave? Sometimes Therapy around the marriage break up may kick up your insecureties. We all have them but when an earth shattering event comes along, it is really confusing. So many questions, why did she leave( that goes far beyond her stated reasons). A therapist can help you see what has happened from different perspectives
The suggestion franciemarie made is a good one. I have advised friends who have moved into an unknown place to look around and see what is there. Bike riding clubs are good, if you are fit enough. A bird watching club can be fun. You get to work on 'your life list' with people and on your own. Volunteering for
Meals on Wheels a couple of days a week lets you get to know people that may be new to you. Visiting with those people who are shut in can lift your spirits, especially when you are greeted by big smiles from lonely people. Do like to draw or paint. This is often done alone, like for me, but it good for sharpening your skills to register for a drawing course -at Adult Ed usually run from your local High School, Community Colleges run summer classes in drawing, jewelry making, pottery on the wheel or by hand.
Are their subjects like the Civil War or Emperors of China that interest you. You will meet student in different age groups. I was the oldest class memger in most of my Architexture cclasses by a leats a decade. I was also older than some of my design teachers....What have you always wanted to do but it didn't fit in your marriage?
The first gain here is that you are doing something you like and helps fill the void.
The second gain here is that you get to be around people who like similar things as you.
The third gain is that you can make good friends and maybe meet that someone special.