The question of marriage between relatives is coming up again and again in this Forum. But so far no one has given the reason why there is a ban on such marriages. All of us know that marriage between brother and sister is prohibited. In fact most people will abhor even to think of such a thing. Ban on marriages between farther relatives is only an extension of the principle.
Marriages between blood relations are called consanguineous marriages. All of us carry good and bad genes. Some are dominant and some are recessive. What is recessive in this generation can become dominant in a later generation. It is likely blood relations carry the same genes, which are bad recessive genes. As both carry the same genes the liklihood of their becoming dominant in their progeny is doubled. One can argue this can happen with the good genes also. There is no rigorous proof for this. Some cite the instance of Parsis. As their population is small consanguineous marriages become inevitable. It is believed that health conditions among them is poor, though, I do not know, whether this is statistically supported. Scientifically advanced countries look down upon consanguineous marriages.
Forum members who already know what I have written above are requested to excuse me.
Now coming to the case of Mithun Dey, no one can penalise you if you get married, unless someone wants to prove your marriage null and void. But who will be interested in that? It may be an overzelous social activist or someone who has a vested interest in proving your marriage null and void.
I do not know how your community looks at such marriages. Children of a brother and sister are often looked down upon as outcastes. You can have such problems if communal bonds are very strong in your community and they are not tolerant towards such marriages.
You may be knowing the opposite thing goes in Haryana with the support of Khap panchayats.
In the film Pakeeza children of brothers get married. Probably among Muslims such marriages are customary. Similarly if your marriage is also permissble under Muslim law, both of you can convert to Islam, go to a Kazi and get married