Same-sex sexual activity is illegal in Sri Lanka and the subject is little discussed publicly. No one has been convicted for over 60 years, but it pays to be discreet. There is no legislation to protect LGBT people from harassment, but the situation is changing slowly, and Colombo has a low-key scene. You can be more open in cosmopolitan areas like Col 1, Col 3 and Col 7.
Equal Ground is a Colombo-based organisation that supports gay and lesbian rights, sponsors pride events, offers counselling services and has useful online resources.