You don't have to go so far as talking about mental illness.
Last season Ross didn't really have any other players around him his own age. We had younger (19- 20) and older (27+). Half of them were fresh out of school and the other half are married with kids. There was Lukaku, but Ross would've known he'd be leaving. Now we've got Klassen (24), Keane (24), Pickford (23) and Sandro (22) so things are a bit different.
I'm not saying Ross wanted to leave because he's got no friends his own age, but maybe if he did have some lads who he bonded with he'd feel more of an attachment to the actual squad. Everyone needs support and peers to connect with. Maybe he knew he'd have that opportunity at Spurs.