It's such a good build-up to a moral, but it's very much needed for him to heal from a relationship that had the expectation of being long-lasting. Yet, he was thrown off course, and the whole built relationship crumbled. This isn't how it should have gone, but I also think this can be used as a push in the right direction. The fear he has is valid because it's a fear he has experienced and is still trying to cope with the aftermath of. I love how his friend said, "Don't keep your head down," instead of something like, "He's not the same person," because what he's saying is to use your experience as a compass and the lessons you've learned in your mind so that you don't close yourself off and keep yourself from living, but as a way to see the patterns and get better at reading those around you.
Ai Ni Dekinai Koi Wa Iya