This question How to politely decline a colleague's wedding invitation given to you personally in office? was closed as primarily opinion based. However, it can be adequately answered with specific expert experience, in this case, "expert experience" with the Sri Lankan/Indian culture.
This is also an on-topic question about navigating the workplace, because the OP is specifically concerned about the social consequences at the workplace of declining a colleague's wedding invitation.
Please cast reopen votes if you agree, or post what can be done to improve this question.
(Disclaimer: I have posted an answer to the question.)