Glassman is shown to be lonely, due to his wife and kids having left him. While their reason for leaving is a bit unclear, it was presumably because he spent so much time on work and caring for his patients.
Aaron has been a doctor for at least 20 years (the exact length of time is unknown). He lived and practiced in Wyoming at one point before relocating to San Jose.
Around a decade prior to the start of the show, he met Shaun and Steve Murphy when they arrived at his office on foot. The brothers had hoped he would be able to save Shaun's pet rabbit, though it had already died when their father threw it against the wall. When Shaun asked if the rabbit had gone to heaven, Glassman awkwardly replied he was sure that was what had happened.
By the time Shaun and Aaron reconnected, Steve had died and Shaun was to be taken back to his parents. He refused to go home, and police were lost on what to do with him. Glassman decided to take the boy in for the night, and promised him tomorrow they’d “figure out the rest." Ultimately, he ended up acting as a surrogate father to Shaun well into the future.