Ginny left him because he never said he loved her and the next day he bought her roses, because he didn't know how to finish things once and for all.
Harry thinks about this while Snape has him pinned underneath him, long, elegant fingers flitting around under his shirt, his tongue finding all the places that drive Harry to madness.
Harry laughs softly to himself, and knows that Snape won't ever say "I love you", not in any tangible way that means anything to anyone else. But Harry knows Severus won't pull away if he holds his hand, that he'll dance with him in the sanctity of their own living room and he knows that Severus will never leave him.
Harry didn't understand the importance Ginny put into "I love you."
He never needed to hear the words aloud. All he had to do was feel it. That was more than enough for him.