Networking Issues

Maybe have a look at this article which may help you go back and start over with the whole homegroup thing.
Additionally make sure you can ping both computers from the other by IP and NetBIOS name.
I've pretty much given up on the Home Group concept and went back to good old Work Group.
Just confirm that both computers are members of the same workgroup (whatever you care to name it) and you need to actually share something.
Other than that it's just a matter of getting your share and security permissions set properly and making sure you don't have an overzealous security suite installed on either computer that may inhibit or prevent networking.
I usually recommend sticking with MSE / Windows Defender and uninstalling any and everything else (security suites) until you get your networking issues sorted.

 

No I am not specifically aware of problems with BitDefender. And since you haven't described any networking issues outside of just creating / joining a homegroup I'm not sure that, that would be your problem.
But.... if you continue to have issues with simple workgroup sharing like access denied or network path not found then you might want to look into it further.
Removal instructions are here and of course get defender and firewall turned back on the Win8 computer and install MSE on the 7 computer.
You can always put it back on if it proves not to be the actual culprit.