According to two other boxers in his group, when they traveled they tried to include him in whatever they were doing, but Tamerlan was the one who refused the offers. It sounds like he isolated himself. People tried to befriend him.
Also, what about his wife? He obviously knew how to get along with someone well enough to marry. She even converted to Islam for him. Didn’t that speak volumes??
People who have a sour attitude often bring it on themselves. Every day we have multiple opportunities to choose to be happy, or we can choose unhappy thoughts. Tamerlan chose to be a loner.