Lance doesn't even realize at first as his relationship with Pidge fades away after that.
She's always been the teammate off doing her own thing, worse than Keith, even. At least he usually shows up to team mealtimes when he's not off with the Blade, but more often than not, Pidge has to be dragged away from her current obsession. Lance had expected things to change once they'd found Matt, but Pidge is Pidge, so she finds a new passion project every time she closes out an old one.
It really sinks in when she stops showing up to movie night, which had turned into "the paladins take turns acting out their favorite TV shows for the others in varying states of awkwardness and skill" after the loss of the castle ship and its ability to project the weird Altean thrillers and Pidge's hoard of laptop-stored movies. Now they're left without even the option to crowd around the 17-inch screen trying to keep up with Pidge's choice for movie night because when Lance tries to hint to her that they miss her, she tells him with no small amount of sarcasm baked into her words that her programming comes first if they want to stay ahead of the Galra. She can't afford to lose two hours distracted by a movie, real or pantomimed.
She huffs off and locks herself in her lion alone for the rest of that night, and they never discuss it after that. Lance stops asking her to come to movie night, and the others begin to agree less often as well until one final night when no one shows up at all, even when Lance waits an extra varga for anyone to show up late.
Maybe Lance is asking too much. Everyone is still bonded well enough to form Voltron as needed, so they must not be doing too badly, and if it bothers anyone but him, they sure don't show it.
So how can it feel like she's already slipped away to a place the rest of them can't follow?