Gay relationship

Hi, I have been having a gay relationship with a younger guy (he is 22) with ADHD for the last 2 years, we started off as the best of friends a year before any relationship developed, he knew I was gay but I thought he was straight. Anyway without going into too much detail here we became more than friends and it was the best relationship I have ever had! I was very careful as not to declare my love to him as thought it may scare him off, a few months back he seemed to back off and when I asked him what was wrong, he said he was in love with me, and had never felt like that for anybody before and found it difficult to deal with, I told him not to worry as I felt the same. Since that declaration, the relationship went gradually downhill and now I have very little contact from him (we live 200 miles apart, although I am a regular visitor to his town) as he is obviously avoiding me for reasons unknown. We have many mutual friends and when they see him he appears in the best of spirits. I am almost certain he is not seeing anyone else, so rather confused as what has gone wrong as never known anybody with ADHD before. He doesn't take his medication anymore as feels he doesn't need it and holds down a responsible job. I would like to know if this is a common symptom in relationships when the sufferer becomes too close to someone?