My feral cat: dilemma

There is a feral cat I have spotted, about last year, crossing a busy street near my house. Then i saw it near the grammar school away from the street. It seems to have found someplace to live away from the busy road, but I cant tell where. It appears on my front porch, having smelled the other outside cat I have (who is now indoors most of the time). This cat is small, sometimes beat up, like its been fighting. Very feral. Will not come near me. It sleeps on the porch in a box I made for it, and eats food and water. Here is the dilemma: on line i found out that feral cats usually dont become tame, dont make good pets, and usually only live a couple years in the wild. I am helping it by feeding it? Should I trap it and take it to the vet? I read that even feral cats who have vet care dont live long. Could I bring it inside the house? I already have a feral cat living inside, who after 10 yrs is finally becoming friendly. I cant see two feral cats indoors - they would fight, right? If I move to an apt, where can I find a place to live with two feral cats? What is the right thing to do? I even read where shooting feral cats is preferred (I cant believe that, but maybe the thinking is that at least they a spared a long, painful death if they are attacked by another animal, or squashed by a car). This cat was bleeding the other day, I found blood on its food dish. Its all black, very mysterious where it goes when its not here. Any advice out there? here is a picture that looks like it (him?) but its not an actual picture.