Okey, he's felt insecure all this time. But he is an adult and he has seen so many times he shouldn't feel like that. I would get if they were middle schoolers or high school but they are both adult. He stills act too immature :') He should have get over it (Ah author-nim) (I understand tho, that feeling. I have done that and it was a bad ending, big regrets..)
being an adult doesn't rid those feelings of insecurities. everyone has a different pace when it comes to terms about their feelings. he knows he loves him but he's afraid of the future. and I'm sure he feels guilty for constantly "stringing him along". i believe he just needs a wake up call to come to terms with his feelings and realize that they could work through any situation that comes their way together.
I can relate to Hyoonsoo to some extent. I struggle to connect with others because of my strong sense of morality and my inability to express myself properly. These issues also made me insecure about being in a relationship. I feel that no matter how much someone likes me, once they truly get to know me, they won't like me anymore because I'm too much to handle. As a result, I push people away and never give anyone a chance. Yet, I still wish to maintain the usual behavior with them, which makes me feel guilty and suffocated.
It's actually not about age. In fact, the older a person gets, the more these insecurities pile up.
You will hate me for this (I've been reading this for a long time, fyi) BUT the bottom is a grown a*s man and he is still act and think like a f*king baby. You are still not sure? After all of things? You still need time to think? Seriously... (I love them both btw, uke is so cute and seme.. Lovely puppy)