How come Peter could remove his suit at the begining of Spider-man 3 but not the end?

In Spider-maan 3, when Peter first got the black suit on, you soon see him with it off, & you see the black suit next to him, & he can choose to take it on or off. But yet; at the end; it's really hard for him to tak it off. He was struggling & it kept attaching to him. How come? Is theree an explanation?

The Symbiote is a living organism. And as it becomes further bonded and attached to it's host, the harder it is to get rid of.

He accepted it at the beginning, there was a bond.
Towards the end he tries to reject it. Sine the symbiote is a living organism as KingD19 says, it can sense these things.

At first he wanted the suit, towards the end he did not want the suit.