Machine Gun Kelly and Megan Fox Leave MGK's Home All Cozy and Close

Machine Gun Kelly and Megan Fox have reached the sleepover stage of their relationship ... which continues to move at warp speed.

The actress was leaving the "Bloody Valentine" rapper's Los Angeles house Wednesday, and they looked super comfortable with each other -- almost like an old married couple -- as he walked her out to her ride. Machine Gun, total gentleman.

As you know, things between MGK and Megan continue to heat up quickly ... they've been getting closer and closer for a month now, and Kelly recently declared his "love" for her on social media.

While there was no make out sesh this time, it's pretty easy to see MGK and Megan are tight as can be with each other. They've got that look in their eye.

It's kinda interesting ... Megan left MGK's pad rocking a Pink Floyd graphic tee, which looks awfully similar to the one her estranged husband, Brian Austin Green, wore last week during a hangout with Courtney Stodden.

We broke the story ... BAG and Courtney are still in the friend zone, at least for now.