"Shark Tank" star Robert Herjavec is pulling out of his biggest investment in life -- he's separated from his wife and headed for divorce.

Herjavec tells TMZ he and wife Diane Plese are already legally separated and we're told they will be divorcing soon. 

The couple married in 1990 and have 3 kids together, two daughters and a son.

Herjavec, who is on the upcoming season of "Dancing With the Stars," says ... "Human Relationships are so difficult ... I wish nothing but love and peace for our family as we move forward from this."

Herjavec has a net worth in the nine figures, so ... the line forms to the right, ladies.