Since official sites rarely provide Sinhala subs for Tamil films, you will likely need to download the subtitle file separately from verified community platforms: Baiscope.lk:
Relive the timeless romance of Gautham and Kundavi! This 2006 classic, starring Bhoomika Chawla , is a must-watch for any Tamil cinema fan. sillunu oru kadhal movie with sinhala subtitles verified