Best of Times (2009)

"Pae" Arak Amornsupasiri stars as Kreng, a lovelorn veterinarian who thinks he still has a chance with his high-school crush, Fai (Yarinda Bunnag), when he learns she's just divorced. But she doesn't remember him from their school days. As the result of a drunken-driving arrest, Kreng is reunited with Fai, who comes to bail him and his best friend (her ex-husband) out of jail. Kreng is sentenced to perform community service, and so he becomes the volunteer teacher for a group of retirees who are learning how to use the Internet. This puts Kreng and Fai in touch with the older couple - Sompit (Sunsanee Wattananukul), a widow who has fallen in love with her classmate Jamrus (Krissana Setthatumrong). The silver-haired gent is a smooth talker, but he has a problem - he's losing his memory.

Source: TMDb