There is church, book clubs, exercise groups (I take yoga), getting involved with a charity (I volunteer for the MS Society), take a class through a Parks and Recreation or Community College Continuing Education. Get a group a friends out for a Sunday brunch once a month. Friendships take time to cultivate. I was a Navy kid and we moved all the time so I was always the New student. I learned to say hello first. Ask questions about others that is an easy way to strike up interest. Then all you have to do is listen.
I went thru the same thing, and I think a lot of others have too. It's now time for you! It sounds like you are already employed, so I would get involved in some type of volunteer work. Church is a good place to start, and you will make new friends. Think of a hobby you've always wanted to try, but had no time for. I was lost when my kids became independent, and then they spread out across the country. Now, I love my own time! I enjoy gardening, long bubble baths, shopping, decorating, etc. I'll go to a movie alone. I gave my kids roots and wings, never dreaming they'd use the wings to fly so far away, but they did. I have always supported their dreams, and still do. Get a puppy, this will keep you busy and it's also a great way to meet new friends, I have 2 dogs. You will adapt, and it will get better.