Seeing team like Manchester United celebrating qualifying for the UEFA Europa league competition always get me sick as a true Manchester United fan. Though been part of the team that will participate in the European competition next season is not a bad one for it is not easy because somany teams are wishing to be there also.
I believe Chelsea team and there fans will not be happy, just like you have said it is truly unimaginable, even winning Manchester City in the FA Cup final was still unimaginable.
There's no need to be fed up with this, mate, because whatever the result and wherever the Manchester United team will compete next season apart from the Premier League, they must still enjoy it and run it well. And as a fan of the team you yourself also have to be more optimistic about the team's performance next season because every season there will definitely be differences so you don't need to remember the things that happened this season to imagine them again next season.