Jennifer Aniston's relationship with Justin Theroux is getting serious!

The men in her life - Theroux and her dad, John - bonded over lobster, wine and their love for Jen at Delmonico's Steak and Lobster House in L.A. recently.

Says a source at the restaurant:

"Jen's a regular here and normally very relaxed. This time she seemed more on edge. She was smiling, but you could tell this was a special event for her."

"John looked very protective of Jen, and when Justin went to the restroom, he put his hand on top of hers," reveals the eyewitness. "It was sweet."

Jen has long been estranged from her mom, Nancy, who wrote a book about their relationship, but values her father's approval more than anything.

John recently confided that the perfect guy for Jennifer has to be not only kind and caring, but "someone honest - honesty is very important."

Hopefully Theroux passed muster.