The suit has a will of its own. It didn't resist before because Peter took it off normally. It knew that Peter would eventually wear the black suit again. At the church bell tower, Peter was taking it off because he didn't want it. The suit sensed that, and resisted. As such, the symbiote knew that Peter wanted to throw it away, so even if Peter "acted normal" in his apartment and just dressed off, the symbiote would have put resistance. Throughout the film, the audience was shown that Peter kept the black suit on while engaging in reckless acts. Therefore, he was likely wearing it at the bar when he attacked MJ. After realizing his error and deciding to rid himself of the suit, he went to the nearby Church to do so. Actually, he finds that this is the perfect spot to get rid of the suit, because, as we can see in the ending sequence, the symbiote has one big weakness: sound. The bell made the symbiote weak, and helped Peter to "break it". This is the same method used by Spidey in the comics, but he uses it already knowing that weakness.
Another answer can be like a reference to the 1994's "Spiderman: The Animated Series", when he accidentally found the weak of the Symbiote in a fight with Shocker in the The Alien Costume saga.