Am I allowed to marry my maternal cousin's son? He is my mother's elder sister's daughter's son.

In some places in the world, this may be allowed, but consult with your elders, parents first, in this matter. Or your local religious authority.

I think that is far enough away to be married. Not completely sure though. Genetically and socially.

Why are you so attracted to a distant family member?

You have 1/2 your mother's chromosomes, and your aunt has the same as your mother. Your cousin has 1/4 (1/2 x 1/2). Her son has 1/8. That should be OK, but you need to know the law where you live.

It will depend on where you live, for not only the laws on marriage but the social acceptance. In most places, yes you should be able to