Hi Nik, to help heal the cuts get him to wash his penis twice a day in a sea salt water wash, this will help clean and heal his penis cuts.
Something for him to try if he keeps getting these cuts, this will help toughen up his skin, you need to make up some brine, for this you just add salt to warm water, when an egg floats in the top its about right, and this you can bottle and store, he mix's half brine and half urine, then he soaks the end of his penis in this, with his foreskin held back, this should help toughen up the skin, and the tougher skin should not then split open during sex.
Just tell him to be brave, I got to this from an idea, you can google will brine and urine toughen skin.
Do hope this helps him.
Good Luck
Does he say he is hitting anything in your vagina that is scratchy? Sometimes guys hit the strings of the IUD, for example. One woman who wrote in, had some genital warts that were scratchy. (Sorry, I'm just trying to put out examples.) Do you have a lot of sex without lube? Do you shave your lady area? (The hairs growing in can be bristly.)