There are many things you can do if you are feeling lonely or left out.
You can plan your own party and invite family and friends. You can invite people you work with. You can invite all of the people you have not called in awhile. You can invite anyone you know.
If you do not have that option, you can volunteer for a cause and meet people.
Or you can get a part time job. Or you can join a book club. Or you can take a class. You can join a gym. You can see what is going on in your community and get out there.
Lose your excuses. You are the only one who can change it. Make the choice to get out there and mingle when you feel lonely.