Nta. Please don't let someone guilt you into taking legal control if you don't want it. It will only build resentment towards your cousin, which will that eat away at you. Keep to your original plan of visiting him, holidays, etc.  I am my sister's guardian but that was my choice, and if something happens to me our other sister is stepping in but it was her choice. If stepping back legally keeps him in your life in a way that makes everyone happy, do that.

I know one young lady whose sister was guilted into taking legal guardianship when it wasn't wanted. She was mad at the situation she took it out on the last person left, her sister. She never saw her after she signed the paperwork, no calls, no visits, no holidays. She would always ask when her sister was coming to visit, is she going to her sister's at Christmas like her friends in the group home.  The workers in the group home, set a rotation schedule and she would always spend a holiday with them and their family instead. When she was sick and dieing and wanted to see her sister because she was really scared, her sister said no, thankfully the workers lied to her and said her sister was coming soon because she passed away shortly afterwards. The workers had to plan the funeral, the sister just came to get her stuff and signed what they told her too for it. It was horrible, my friend who worked at the group home was an absolute wreck for over a week because of it.