EXCLUSIVE

Ariana's Ex-BF Nathan Sykes She Left Me Out of 'thank u, next' ... That's AWESOME!!!

One of Ariana Grande's famous exes is beyond thrilled he didn't make the cut for her new hit song about past romances ... so much so, he couldn't contain his sense of relief.

We got Nathan Sykes of The Wanted Wednesday at LAX, where we asked how he felt about not being named in Ari's song "thank u, next" ... which name-checks the likes of Big Sean, Ricky Alvarez, Mac Miller and, of course, Pete Davidson.

Nathan, who dated Ariana briefly in 2013, hasn't heard the track yet ... but after we described it, he breathed a genuine sigh of relief. Seriously, you have to see his reaction -- pure joy.

The song's basically about what AG's learned from each of her ex-BFs. So, we had to ask Nathan what HE learned from her.

We're not saying he shaded her -- he actually showed Ariana a lot of love here -- but let's just say there was a looong pause after our question.

As for her being single now? Nate's good.

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