come to a head idiom (also bring something to a head)
到紧要关头
If something comes to a head or someone brings something to a head, a situation reaches a point where something must be done about it.
Things hadn't been good between us for a while and this incident just brought it to a head. 我们之间的关系恶化有一段时间了，而这件事更是雪上加霜。