Feeling behind in life

I feel behind in life. I know it’s just a thought. I know intellectually that we all have our own timeline and that I’m just where I’m supposed to be, but it doesn’t feel true at all. I’m 48, single, never married, always had very short relationships, and no kids. My business is not making enough money yet to live a lifestyle that I would like as right now I am not sure how to pay my rent.
All my friends are or married, or with kids, or both, and have a good job or successful business, so I compare myself.
My circle is very small and I don’t see them often. They see each others with the kids, so I’m not very included.
I feel I don’t belong.

How not to feel behind in life?