The Romas threw away a lead to lose at home to the National League South title chasers.
Gill’s team have now only won once since October and their promotion push stalled at Twerton Park.
The manager spoke to the club’s YouTube channel after the 2-1 defeat and said his side really should have done more.
“This is the most disappointed I have been for a very, very long time,” said the former Birmingham City player.
“At half-time I thought the game was there for the taking. We were by far the better side.
“Then we let in a poor goal after they broke our line, straight down our middle - it was not a nice one to concede.
“In the second half we just didn’t look like a Bath City team at all,” Gill added.
“I was looking for leaders but there was nobody driving the team. At times our decision making was farcical.
“I know Billericay are a top three team in the table but I through they were there for the taking. I’m so disappointed.”