This is a really Old story, (maybe 10-12 years?)
The main Protagonist (80% sure his name was David) meets a
shy young introverted girl in College. She asks him to tutor her (As all pretty ladies do) they began dating.
After some time in their relationship, they went to see the girls mother at her home (for Christmas maybe?) The family hit it off. And there was definitely Chemistry between the mother and the BF.
After spending weeks with his girlfriend and her mother, the boy flew to visit his own family (Again, must have been Christmas time) But before returning to College as he was suppose to, Our Hero decided to surprise his GF and the mother with a surprise visit. But as he got there, he was the one surprised, his GF was going down on her Mother. Shocked, betrayed, he decided to leave quietly, leaving a breakup note. He got back to the University, withdrew from all his Classes, and didn't answer the phonecalls and voicemails and Emails, all from his frantic GF. After a week or so, he got a visit from his GF's be mother (he had a Crush on her) Her mother explained that the GF was in a Catatonic depressed state, her relationship with her daughter (turns out she was adopted), that she really loved both of them, and was prepared to leave forever if it meant they got back together, and as a Sugar on top, gave him a Blowjob to prove she was serious.
After much soul searching, the boy decided to take a chance and got back to his GF. After an emotional tear jerking reunion (with make up sex!) The mother was prepared to leave, but was stopped by our Hero, telling her that he loved her too.
That is as far as my memory go. All in all, it was rather a short story with loads of sugary writing. Also I seem to remember the author had only one story on his profile.
Looking forward to your help!