Affiliate Marketing Secrets

I have three GMail accounts, one for a non-profit I support, one for an affiliate business of mine, and one for myself.
For the last several months, I’ve been able to keep three separate tabs open in my browser, and look at my mail in all three accounts at will.
Suddenly, yesterday, they are all connected, so that when I open one, it closes the others.
More importantly, when I close one, it shows me the other two and asks if I want to open them.
I set up three different accounts–with different owner names, user names, passwords, email addresses, etc.–on purpose. I don’t WANT them to be connected in any way.
What can I do?