Jose Baxter's first goal for the Blades gave the visitors a half-time lead, yet after the interval there was no stopping the home side.
Weir said: "It was the manner of the collapse in the second half that hurts the most.
"After being comfortable in the first half the second half was very, very disappointing. The manner of the goals makes it doubly disappointing.
"I think we contributed in a big way to our downfall, there's no doubt about that. The level of the goals we conceded and the level of the mistakes. It is going to be difficult to win a game of football when you commit that level of mistake.
"We were on top in the first half, but a game of football doesn't last 45 minutes, it lasts 90 minutes. It was the reaction to their first goal that was the worst thing about the game. We have got to be stronger than that and obviously that is another disappointment.
"We did well in the first half and got ourselves in a good position, but you get nothing for that."
- Sports & Recreation
- Kieran Agard