Robin Thicke -- I Haven't Given Up on Paula

The fat lady hasn't sung in Robin Thicke's marriage ... at least according to him, because he has had time to think and he's now determined to win Paula Patton back.

TMZ broke the story ... Paula called Robin on Friday to tell him she wanted a divorce ... and Robin jumped on a plane and flew to Canada and tried in vain to convince her to change her mind.

Sources connected with the singer tell TMZ ... Robin desperately wants to save his marriage. We're told he's resuming his tour on Thursday where he's performing in Washington D.C., but he will NOT go out on the town -- something he liked doing in the past.

We're told he wants to convince Paula he can change and be a good husband. The surreptitious ass-grabbing is a thing of the past.

Sources also tell us ... Robin is really concerned about their son. He does not want him raised in 2 separate homes.

The couple released a statement saying they have separated ... but our sources made it clear ... she wants a divorce.