this is an abbreviation of: “to be so mother f*cking god damn
lonely”
it comes from the song abbreviation ‘tbsl’ (To Be So Lonely by
Harry Styles)
this slang/abbreviation is used a lot in wattpad comment sections when people feel really lonely compared to the probably romantic scene they are reading.
it is widely used by (mainly directioner, harries, louies etc) wattpad users and is an inside
joke from within the fandoms