There's so much misunderstanding with Shizume's character. He is just one representation of the struggles gay people face. He is not ready to come out because of maybe his circumstances at home or various other factors. Fortunately for him, Tomo is patient and is ready to wait. They have the grounds of a healthy relationship, no one is forced to do anything just to keep the relationship look good. They communicate what they can and can't do and look for compromise.
I like to quote what Tomo says in here because he is surprisingly very emotionally intelligent and a good communicator:
"If you don't tell me that you can't do the things that are impossible for you, my desires will turn into your quota." and that's basically how they operate. Shizume doesn't force Tomo to do anything, Tomo simply does it willingly because he loves him.