Frankie Grande sent folks into a frenzy Wednesday when he said he went on a "double date" with Ariana and Mikey ... but now he says he was not implying Ariana and Mikey were an item.

Frankie started backstroking Thursday, saying ... "My sister is not in a relationship. Everyone relax. She is very much single."

Now, Frankie says his "double date" comment just meant Ariana and Mikey went out for dinner with him and his boyfriend, Hale Leon.

Aaaand breathe, everyone.

BTW ... Ariana and Mikey have been dogged by dating rumors ever since they collabed on her track, "Boyfriend" -- which probably explains why Frankie's comment caught fire.

As you know ... Ariana's got a long list of famous exes ... including Pete Davidson, Big Sean, Ricky Alvarez and Mac Miller. The bad news for Mikey is he's NOT dating AG (in case that wasn't clear), but on the other hand ... he won't be on her list of exes.