How do you deal with the loneliness as you grow older?

As I am growing older, I feel more and more alone. Most of my friends are either getting married or seem to be well settled. However, I am on the adventure of applying for a phD. But throughout the process ( application or studying time) I feel more and more alone. I keep having doubt that whether I am taking the right step or not. I really don't know how to curb this sensation of deep loneliness or aimlessness. Is prayers going to help? I find myself without any proper supervision or guidance which makes the path more unstructured and confusing.