I don't think you have actually seen any Northeast people.
The opposite. BD will support India against China.
And yes, BD has massive water issues with China.
Haven't you heard of Diego Garcia? Bay of Bengal?
https://www.heritage.org/asia/commentary/how-bangladesh-can-improve-indian-ocean-security
In 2016 Bangladesh’s shipping minister insisted his country needed “stronger bilateral relations with India to save Bangladesh from any external aggression,” noting that Pakistan was “hatching a conspiracy against us.” India and Bangladesh currently conduct joint military training exercises and in 2017 agreed to further increase defense cooperation.
Bangladesh might also be considered for observer status at the annual India-U.S.-Japan Malabar exercises.
Actually I have met many Northeast Indians. 100s of Northeast Indian students come here every here to study medicine in Bangladesh. They don't really have positive attitude towards the mainland Indians.
I propose the following measures for effective cooperation between Bangladesh and India,
- The Eastern Command of Indian Army should be disbanded. Bangladesh Army will take care of the security of Eastern India and Northeast.
- Eastern Air Command of Indian Air Force should be disbanded as Bangladesh Air Force can very well take care of the air space of Eastern and Northeast India.
- Eastern Naval Command of India Navy should be disbanded. The security of Bay of Bengal will solely be Bangladesh Navy's responsibility.
- All the military assets of Eastern and Northeast India should be handed over to Bangladesh military as Bangladesh will be far more efficient to command the region because of shared culture.
- The funds invested by Government of India to maintain these military assets in the region could be diverted to development programs in India for poverty reduction.
- The less developed states in Eastern and Northeast India like Bihar, West Bengal, Orissa, Assam, Tripura, Mizoram, Manipur could be given on a lease to Bangladesh for 99 years to have them developed under Bangladesh model. We will utilize our development experience on these states. (Optional but recommended)