After the last club football ends (which is normally the European finals), although I tend to lose interest after the Albion games unless there's something interesting going on. I don't regard international fixtures as being part of the season any more than I would regard the world cup as being part of the previous season, it's a postseason tournament / fixture.
It depends:
If we were relegated, the season ends then.
If we're safe (or promoted, having been in a lower division) then it ends when the Football League playoffs end.
But this season, because of two English clubs in the final, I'll have to go with the CL final.
It nevers ends for me, as I'm betting on leagues from around the world every day (only a quid or two). Some days I'm willing the ball over the line of a Tanzanian/Nigerian/Armenian league game
When they stop showing it on telly. So never, really.
Its been quite a dull week with nothing on. Looking forward to the Playoffs now, and the European finals, then England. If I get desperate I might watch some of the Female World Cup I suppose.