Your daughter is 29 and a adult. You cannot control who she sees.
This relationship does not sound good to me especially when this man is so much older and has been married 3 times before.
But what can you do? Nothing much. Make it clear you disapprove, and give her your reasons why. Then, leave it, don't nag, you will just drive her away.
Support her when she needs you, listen if she wants to talk, just be there for her.
Its hard when you care for her so much, and you can see she is making a mistake, but realistically you cannot stop her.