"I don't think any of us thought this was the right guy for her," a source close to the busy star, 47, tells PEOPLE in this week's issue. "He's a very nice man, but he can't keep up with her. She's a force of nature."
Sally, 43, who declined to comment on the case to PEOPLE, is requesting full custody of the couple's unborn child.
The source says Shepherd, who is mom to 9-year-old son Jeffrey from her first marriage, to Jeff Tarpley, made no secret of her desire to have another child via surrogate.
"She was open that this would be the only way she’d be able to have another baby," says the source.
For much more on the end of Shepherd's marriage and what's next, pick up this week's issue of PEOPLE magazine, on newsstands Friday