Draco Malfoy & Severus snape
Every year since he found out it was an option, Draco would stay at Spinners end.
Until 3rd year (or which ever year you want),
When severus took in harry after he found out about his situation with the Dursleys.
However, with Dumbledore insisting on harry being with the dursleys because of the blood protection harry gains from being with Petunia, Snape is keeping the fact that Harry is with him a secret.
Which means that's school holidays could not be spent at spinners end anymore.
For most this wouldn't be an issue. But there's a reason Draco needed spinners end, needed a place away from Malfoy Manor. [Insert abusive or controlling parent]. Draco never told anyone about it because it made him weak and Malfoys were never weak.
So he never tells anyone. Severus is focused on helping Harry so it take him a while to realise that his godson hasn't been his usual self.
[Insert more angst]
[Followed by a happy ending]
Severus now has two sons to take care of.