TMZ spoke with A.J. Lamas … who tells us he DID venture over to his ex-GF's Los Angeles home on January 11 at 2 AM to "discuss" their recent breakup … and entered the home through a window, as he did habitually when they were together.

Basically, he admitted to breaking and entering … but in a good way. Once he got inside the home, A.J. says he saw another man in his ex's bed … and tells us, "That was all I needed to see." A.J, says he attempted to leave the home without "incident." But seeing his ex with another dude made him REALLY thirsty, so he went to the fridge and grabbed a beverage … which turned out to be a Four Loko alcoholic energy drink.

Of course, A.J.'s ex tells a different story … claiming Lamas had NO BUSINESS being in her home … and insists he tried to trap her in a bathroom so he could spout off about their failed relationship.