Please try and understand that
@HeinzGud is trying to explain the inertia of the Sri Lankan people's thought process. They are anti-India due to our mishandling of the Tamil-Sinhala ethnic conflict, and these sentiments will not be changed so easily just because we are not doing anything to undermine their interests right now.
Crowd mentality has an inertia far too great, and the mindset of a population can not be affected so easily.
If we want to change this, it is going to take a generation of no mistakes and relentless efforts from our sides. If we try too hard to pressure the Sri Lankans the wrong way, to keep them from falling in Chinese hands, then it is going to blow back in our face. The current Chinese overtures will lead to greater involvement of China in Sri Lanka, and we need to accept this to an extent. We need to accept it because we made a mistake with the way we handled (mishandled) our ties with Sri Lanka in the past. If we try to stay in denial mode w.r.t. to this, we are only going to push the Sri Lankans further into the Chinese orbit.
You talk about supporting the Sri Lankan tamils. Truth is, its none of our business. We need to deal with Sri Lanka as a a country, and we need to avoid taking sides in an ethnic conflict, which was the mistake we made before.
Stop giving ultimatum to the Sri Lankans, asking them to mend their ways and reject Chinese overtures. We are only going to make them more defiant with the high-handedness in our approach. We need to be smart about this. We need to accept more Chinese influence in Sri Lanka than we are comfortable with. We need to give the Sri Lankans the autonomy to decide between balancing ties with India and China or acquiescing to the Chinese at the cost of ties with India. The option of them rejecting China in favour of India was closed by us with our short-sighted policies, so we need to stop pushing for that option.
Over time, the people of Sri Lanka will see reason, and will try to balance ties with India and China.
That is the best case scenario for us in the medium term. If we hope or try for anything more than that, we loose.
They have a good reason for it, unlike the Pakis.