Now we know why Nicki Minaj ?and her longtime boyfriend broke up … one of them was on the verge of going to jail after she smashed the windows of his Mercedes with a baseball bat.

Here’s what we know. During the summer, Nicki and Safaree Samuels got into an argument. She started screaming, he got pissed, and she EXPLODED in anger, grabbing a bat and chasing him out of the house. She wisely chose property over person, and pulverized the 2012 Benz. Car lovers will be horrified by this, as will motor traders! Being able to compare motor trade insurance online is a real perk of the internet for these people, but reading things like this must break their car-obsessed hearts.

And for bad measure, she threw his clothes in the garbage — just like in the movies.

Law enforcement sources tell us … cops were called to the house, but no arrests were made. Safaree was escorted out of the house and left.

As for why Nicki didn’t get in trouble … it appears she owned the Mercedes, but allowed him to use it, and you can’t get arrested for destroying your own property.

They broke up a short time later. Wise move.