Block? Are you sure, he's actually in my circle of friends on google. When he sends something, I usually just like it, but as of lately I just swipe it away from my notifications.
'I understand that, as a friend, you feel the need to share things with me. However, it's been getting too much for me lately. Could you therefore discontinue sharing these things with me? Thanks in advance.'
This is one way of politely asking him to stop. There are probably better ways of asking him since English is not my native language, but this is roughly what I would say.
Thank you guys for the advice I'll give a little time, and I'll say something along those lines. I'd disable the notifications if I knew how, so that I could view them later whenever I go to G+