The Teessiders dropped to tenth on the English second tier table after the weekend's 2-0 home loss to Brighton & Hove Albion, making it their 13th defeat in their past 17 league outings.
Saturday's loss to the Seagulls saw Boro go eight points out of the top six and Australian defender Williams was well aware just how bad things have been at the Riverside Stadium recently.
"It been a painful season," he told the Evening Gazette.
"It's disappointing to say but first and foremost it is just horrible that we are destined for another year in this horrible league next season.
"I know the fans feel hard done by. I feel the fans frustration. But we are hurting too. We all know how bad it is.
"Personally I am angry, upset, and disappointed. With this team, this manager, this ground... we shouldn't be in this league."
He added: "There are four games left and we need to finish on a high and then take that into the new season. We don't want to end on a sour run like this. We need to finish the season as strong as we can then have a break and regroup and go again next season."