Worry about my 30 yr old daughter

If it is any consolation my DD was the same. She had a string of long but unsuitable relationships. The last one was 5 years and was a disaster. Fortunately they were both living in her flat so she kicked him out but was devastated.
We both spent the coming months in tears.
Then when she was 35 she met someone who is lovely. She married at 39 and they seem to be very happy.
Maybe like my DD yours is just finding out what she doesn't want. As she gets older her confidence could grow.

At the moment all you can do is be there for her. Many is the time I have sat on St Pancras station in tears waiting for the train home. Don't despair she is still very young by today's standards. Just be thankful they weren't married.

She's an adult so you don't need to do anything - except be there for her. Remind her that she won't always feel so bad.

Nothing you can do, except be there for her.

We are in the same situation with both DDs, if I offer advice I get my head bitten off, so I’ve learnt to be comforting with mouth firmly shut.