Arnold Schwarzenegger -- Maria Confronted Me About Love Child In Therapy

Arnold Schwarzenegger says his estranged wife Maria Shriver confronted him about his secret love child during a couple's therapy session and that she'd suspected for years ... according to his new book ... but the good news -- Arnold assured Maria he was still "turned on" by her.

In the book, obtained by the New York Daily News, Arnold says Maria took him to couple's therapy in 2011 -- the day after he left the California governorship. He believed he was there for routine marriage counseling -- instead, Maria asked him point blank if he slept with the maid and spawned a love child years before.

Arnold admits, at first, he made a slew of excuses to his wife -- but then copped to everything: cheating, the secret child and supporting his baby mama financially ... calling it a huge screw up.

Before Arnold fessed up Maria intimated the maid had already told her.