While I do support Marxists and anarchists working together against imperialism and capitalism, communism and anarchism are not compatible. Anarchism, oversimplified, presents a world of interconnected horizontalist cells, essentially a world of petty bourgeois cooperatives. Communism seeks total global collectivization across all of society, to create a classless world. The reasoning for this is that Marxists hold to dialectical materialism as our worldview and toolset for changing the world, whereas anarchists do not.
This strikes me in particular because I used to consider myself an anarchist. Part of my growth into a Marxist was simply understanding how historical materialism works, as presented by Engels in Socialism: Utopian and Scientific. I recommend giving it a read when you get the chance, and really pay attention to how Engels describes the transition to socialism and communism.