When people reveal to you who they are by their actions, believe them!
A source of deep woundedness is betrayal and deception. Last night, I was reading a legal statement of a person who committed a known marital infidelity and eventually bigamy in a span of 4 years. As expected, the legal statement was a mixture of some facts peppered with lies, exaggerations, and fabrication to cover up the tragic sin of adultery/bigamy. Despite the obvious offense, the person had the audacity to file a legal, non-biblical divorce against the wounded spouse. This person attends church worship and claims to be a believer.
Sadly, we all know many people who claim to be Christians. But they live in unrepentant, ongoing sin. In the case above, it's not the responsibility of the betrayed, believing spouse to punish/judge the offending spouse. It's God's job. Someday, the adulterous spouse must face God with the sins and their consequences. And God is a just God.
The Word of God judges; not us. What is my place to discern is, one may claim to be an apple tree but if the fruit coming off is a banana, then the person is deceived. One may claim to be a Christian, but the actions/behavior ("fruit") can say otherwise. Jesus presented that truth so clearly.