He posted comments from "Amina Arraf", supposedly a lesbian Syrian blogger, but actually student Tom MacMaster, 40.
When "Amina" was reported detained, activists campaigned for her release.
Mr Graber, who wrote under the name Paula Brooks, is no longer associated with LezGetReal.
In an apology to its readers, one of the other owners, Linda Carbonell, wrote: "The past three days have been devastating for all of us on LezGetReal. 'Paula Brooks' has been a part of our lives for three years now."
Betrayal of trust Mr Graber told the Associated Press news agency he set up LezGetReal to advance the gay and lesbian cause. He said he felt he would not be taken seriously as a straight man.
"LezGetReal was not meant to be deceitful or con anyone," he said.
On Monday, Mr MacMaster, originally from the US state of Georgia but now a student at the University of Edinburgh, said he was sorry for posing as a Syrian lesbian.
He has now re-titled the blog, originally A Gay Girl in Damascus, simply as A Hoax.
In his second apology, he wrote: "I never meant to hurt anyone. I am really truly sorry and I feel awful about this... I betrayed the trust of a great many people, the friendship that was honestly and openly offered to me, and played with the emotions of others unfairly.
Ali Abunimah Electronic IntifadaThis deception... has sown confusion, distraction and absorbed energy and attention at a time when real people are in danger in Syria and in other countries in the region.”
"I have distracted the world's attention from important issues of real people in real places."Activists and bloggers angrily criticised Mr MacMaster when he admitted he had created the Amina blog five months ago. In it, he described life in Damascus and the current political unrest.
In an open letter to Mr MacMaster on the OGay Middle East blog, activist Sami Hamwi wrote: "Your apology is not accepted, since I have myself started to investigate Amina's arrest. I could have put myself in a grave danger inquiring about a fictitious figure. Really… Shame on you!!!"
'Stand-up guy' Mr Graber defended his actions, saying he had helped unmask Mr MacMaster by tracking his posts to computer servers in Edinburgh.
"He would have got away with it if I hadn't been such a stand-up guy," Mr Graber told AP.
Entries on the Amina blog covered "her" social life and relationships, but also criticised President Bashar al-Assad and spoke about "her" role in the growing anti-government protests.
On 6 June, a post purporting to be written by Amina's cousin said she had been seized by armed men believed to be members of President Assad's Baath party.
The news was widely reported, including by the BBC. Bloggers and activists launched an online campaign to secure her release.
Mr MacMaster told BBC Scotland he had wanted people to listen to the facts without paying attention to "the man behind the curtain".