Hi I have gone through your query, i will try to give you suggestion which will be helpful to you. It sounds like you have some irritation of your foreskin causing the small cracks. These type of cracks can be quite painful. Basically, they re like small paper cuts that are reopened everytime you pull your foreskin back and cause the skin to tighten up. I would suggest you, its nothing to panic, use cotton underwear, using a moisturizer may help. As it is cracked if try to push the skin crack can reopen so, avoid doing so for two days or so. I think he might have tried to push it regularly, that might be the reason it has not healed for week. I advice you to follow the measures mentioned he should be fine. It may also have been caused by insufficient lubrication during sex. Try using more lube and giving your penis more time to heal. Masturbation does not cause infection, it may be small cut that has occurred during the act may be responsible. If it is infected a course of antibiotic is adviced. For that you need to see doctor for examination and further help. I hope this suggestion might be of some help to you. I here you to help you in case of any further queries. Wish you speedy recovery. Take care.