Does patient suffering from mental health illness act like living in fantasy?

Hi doctor,

This question is not about me. But it is about a family member that I truly love and want the best for him. For the past years, my brother has had a big crush on his manager. He would always talk about her when he would come home from work. He would talk about her constantly. Sometimes even saying that she also likes him and that he knows they are going to end up together. He had the biggest crush and still till this day talks about her. He lost his job a few months ago and started acting weird. His manager is a different race. So when he was home after he got fired, he would constantly be outside wanting to get tanner because he said thats the way she likes guys. To be tanned how his old manager's race is. He would sit outside every single day wanting to get sunburned. He did indeed. Then weeks went by and he told my mom that his mission of sitting down outside was over and that he will start going to walk instead. At this moment all he does is wake up and go walk anywhere and walk to different places for no reason. He constantly says that he is married already with his old manager and that he is moving to another city. He says the same thing every time. He leaves since the morning and walks everywhere and comes back till the night. He does not do drugs but has a past of doing drugs. He used to drink every weekend before he started doing all of this. He would drink coffe every day before work. And on weekends drink alot. I and my family are concerned about him. We do not know what is wrong with him. He does not do drugs. He drinks sometimes on weekends, not often anymore. He says he is married and that he makes a call to someone and they pay all his bills. He leaves every day and walks anywhere. He knows what he does, he is aware. But we do not understand why he thinks stuff that is not in fact true. He is living in a fantasy.