In 1796 his future wife Lea Salomon, a granddaughter of Daniel Itzig, also joined the Akademie; but they had probably met before that.
In 1804 Abraham married Lea in Hamburg, where he managed an office of the family bank.
Somewhere around this time he seems to have acquired from Lea's acquaintance with the musician Georg Poelchau a number of manuscripts of C. P. E. Bach (of whom Poelchau was the executor), which he gave to his aunt, the musician Sara Levy, who subsequently donated them to the Singakademie.
The private bank which later was renamed into Mendelssohn & Co., existed on the Jägerstraße in Berlin from 1815 until the end of 1938, when it was liquidated under Nazi pressure.
In 1811, the French occupation of Hamburg and decline of trade caused Abraham and his family to return to Berlin.
Both Felix, born 1809, and his elder sister Fanny, born 1805, showed signs of remarkable musical talent and this was encouraged in both of them, although Abraham felt, conventionally, that whilst it might lead to a career for Felix it could only be a pastime for Fanny.
Abraham and his wife are buried close to three of their children and their graves are preserved in the Trinity Church Cemetery No.