This PMV tells the story of what happened to each of them after Hogwarts. Yonal's part, in particular, he left Hogwarts during 5th year to attend his mother's funeral back in the Philippines, hence why he never had a 'proper (wizarding) education' but instead, finished their education in a muggle school. He maintained contact with the two for as long as he could but for some unknown reasons, they started gradually fading. Severus was the first to cut ties with him.
He never found out about Lily's death until a few months after when Charlie Weasley handed him a Daily Prophet newspaper. It's no wonder she stopped sending him letters.
The summer of fifth grade, Snape comes home and opens the door to see his mother's feet dangling and swaying in mid-air, and after the burial Snape remembers why Eileen picked the very day he returned from school to hang herself, and believes that it was his mother's revenge on the son who had done nothing to help her in her life