The first step to solving any problem is to acknowledge it exists!
Second step is to define it correctly. What does gay porn manga give you? And can you get that elsewhere?
Sometimes a person does need something that's just mind candy, to function as something to make your mind do, to stop it spinning and stressing over stuff. A hobby that requires you to do more thinking doesn't do that - it just gives you more stuff to spin and stress over.
But in that case, the question is not "what do I do instead of gay porn", it's "how do I change the thing that is stressing me out so much that I need to keep my mind off it/escape from it/rest my mind by looking at gay porn?"
I, personally, do not look at gay porn manga (or any kind of manga). I do, however, read trashy romances. They probably perform a similar function for me: they are so low-stress and low-emotional-and-intellectual-input that they help my mind rest.