Six years and a baby won't slow down their sex life.  Robin Thicke reveals his key to keeping his marriage with wife Paula Patton in tact...is good sex.  Not mad at that.

Deets inside....

If you need to know the key to the perfect marriage in an era full of divorces, crooner Robin Thicke says his secret is simply good sex.  He and Paula are high school sweethearts so have been together a minute.  But the thirty somethings' hectic schedules barely allow time for them to spend some QT.

The "Sex Therapy" singer told Us Weekly at Sunday's AMAs:

"My wife is an actress, a mother, and a wife and I am a husband, a father and a singer so we haven't seen each other a lot the past couple of weeks," he continued. "We won't see each other a lot until Christmas and it's very difficult, but the only thing that gets us by is having great sex together. There is never enough [sex]. When it does happen, it goes on for hours."

"It's the only way to keep everything on par."

Sounds good to me.  And when asked if they're putting their bedroom practice to use to get baby #2, he said:

"Once you see what a woman goes through having a baby, you know what real compassion, understanding, patience is all about, so that's absolutely what the album is about.

"[Another baby] is not something we are planning on doing.  I think anybody who has two babies…God bless you!"

Check out Robin's latest vid "Love After War" off the album of the same name, starring his fave sex subject herself--Paula:

The album drops December 6th.