Ariana's getting a little emotional, being on the road all alone after all she's been through recently ... and she took to Instagram to post about her loneliness ... and about "letting go."

She wrote: "Sometimes, the reason for letting someone go is because they can’t help but hurt you during this phase of their life. When you love someone deeply, you learn what demons live within them and you realize they are hurting you because they are hurting somewhere within themselves. They are fighting a battle within and may not even know it, so they take it out on you and fight you. Decide to let them go, but not because you’re being petty and resentful. You let them go because you really believe that the both of you can find the healing you truly need without being together and hurting each other in the process. Letting someone go doesn’t mean you stop loving and caring about anyone. Letting go means you’re choosing freedom over the illusion of loyalty.”

The singer is preforming in New York right now, on her Sweetener tour and we kinda think she's missing her hometown boy Pete Davidson. Her ex has, of course, since hooked up with the much-older Kate Becksinsale and is currently in LA after having just met HER PARENTS! In fact, we spotted him last night leaving a club in a High Times hooding, smoking a cig and drinking a Red Bull. He looked a little worse for wear ...