The answer on that one is simplicity itself: LEAVE. You are not bound to offer an explanation or justification for your departure, and you are not answerable to anyone for your decision. No one said that, when you became an atheist, that you were obligated to defend atheism to every bovine-brained buffoon who came along, challenging our disbelief in their precious deity. Not everyone is AronRa or Matt Dillahunty and has the skills to counter arguments in real-time, and it's worthy of note that they and others like them weren't born with that gift but cultured it over many years.
I have done my own share of debate and discussion regarding religion on another board for several years, before that board's lack of supervision and the obvious opacity of the believers' attitudes made me turn my back on that site. It was enjoyable to work with other atheists there, formulating arguments and enjoying our shared bonhomie, but ultimately, the site's lack of discipline spoiled it for me. I pulled the plug, leaving no trace of my participation, as many of my fellow non-believers did, and I don't regret my decision for one second.
So ... will they figure that you bailed out because you were frightened / insecure / didn't have answers? IT DOESN'T MATTER! You have no control over what they think any more than they have control over you, unless you grant that control to them. You can engage in discussions here for your own amusement and/or education. If you wish, you can work to culture a level of expertise of information and debate skills so that one day you can go back and level the poor arguments the believers offer ... or not. You might also learn the Socratic method, such as what Peter Boghossian promotes in his book, A Manual for Creating Atheists, and subtly sway them to our side ... or not. Your existence does NOT depend on them or what they think. So what if they believe that the Earth is 6,000 years old and that mankind came from a dust-man and a rib-woman?
They're full of shit. Fuck 'em.
I don't debate Christians. They seem to think that if they disprove Darwin it has to mean "god did it." Then they do not understand when you ask them "which god?" The obvious choice would be the god you were born with, i. e. the religious system you were born into. Some of them do understand this however and they think all religious writings are referring to the same god and same creation. The problem here is that religious writings (or scriptures) are so seriously flawed that it's hard to believe any gods were ever trying to get a hold of us and get our attention.
What all the writings do show is the exact opposite. We are trying to get a hold of god.
I have a Yahoo mail account as well, generally going directly to mail.yahoo.com. Logged in, it's generally ok. (I use Adblock Plus.) When I actually sign out (say, from a private window on someone else's browser) I've noticed the home page crammed with "tabloid" clickbait headlines interspersed with "newsy" ads.
Even if some headline intrigues me, I don't want them having the "satisfaction", er, marketable data of that click. I'll search for that news story on my own.