What I can say is that keeping a relationship trough internet is difficult. Being separated....with distance between is just a way your heart to die slowly.

I suppose your beloved one has a reason for not answering your questions. Don't loose heart.

You say: "just exactly as he retired from work,he also stopped our communication"

Well you should know that pensions/retired pay/ in Japan is extreemly low. This is the main reason for the high rate of suicides.
Maybe your boyfriend still sends you money from his savings or sth like this. Maybe he thinks that when his savings end or when he comes to a point when he can't send you money anymore you will not need him. SO IF you LOVE him then you should talk to him and tell it to him. If you have the opportunity to take a plane and go to him-do it.

Maybe you both need to talk...you know sometimes even one or two words are enough.

Good luck and all the best!!