The speaker is grieving a relationship that ended in silence. There was no final conversation, no proper farewell. The two people simply drifted apart, or were cut off from each other, and the speaker says that is what hurts most. The unsaid words weigh more than the breakup itself.
The mood is quiet, raw, and a little bittersweet. The speaker still manages to say thank you, naming both "the happiest and the toughest moments," so the gratitude sits right next to the pain. The short, plain lines and the casual, lowercase style make it feel like a private note rather than a polished piece, which makes it sound honest. The last two lines land with a small sting. Calling the other person "just my another lesson" suggests the speaker once hoped this person meant more, perhaps something lasting, and is now trying to accept that they were a stepping stone. The phrasing reads as both a way of coping and a lingering ache.