This is about social skills and it's a long answer. "Trust" is about a firm belief that someone will listen to your advice, behave good or learn from their mistakes. When someone did something wrong but we forgive him/her, then we can still trust them, especially if they made mistakes a few times. However, if they keep on repeating their same mistake and keep on breaking their promises, then trusting someone can become hard. This is about probability. If they just made a mistake once, then it's unlikely that they'll repeat the same mistake. However, if they keep on repeating the same mistake, then it'll be more likely that they'll continue their mistake. Whether someone can still trust or not, it also depends on their psychological problems. If someone is psychologically ill, then that means that they're weak at controlling their emotions. In this case, they can soon get very angry and might be unable to trust even if they repeated their mistake only a few times. If someone is psychologically well, then that means that they're strong at controlling their emotions. In this case, they can try to stay calm for a while if possible, give someone some more chances unless if they already repeated the same mistakes many times already. If we can't trust someone anymore, it could be because they repeated the same mistake many times, their problem size, and/or people's psychological problems of whether they can control their emotions or not. If you can't trust someone anymore, then it'll be hard to trust them again. Pushing yourself to trust someone is the only way to replenish your lost trust.