He didn't. Towards the end of the war, he started a relationship with the artist Vera Willoughby, with whom he lived after demob. According to Nico (in his correspondence with Sharon Goode between 75-78):
"Peter entirely loved her, and I would say it was entirely mutual. When he was demobilised they set up house together and they lived together for a number of years. Certainly in Epping, maybe London before that. I think his first business was to do with old furniture etc. (...) I saw Vera from time to time and much liked her. The so-called break came after Michael was drowned: but it was really Vera insisting that Peter should not throw his whole life away etc. Heaven knows (I never really spoke about it) how painful the parting will have been: but Peter greatly helped save J.M.B.’s reason and from the moment he entered the book trade they obviously had an extra bit in common. Vera did not cut herself right out, in fact she illustrated many of the books that made Peter’s name as a publisher of exquisite taste if poor sales!"
After he learnt the publishing trade (with Barrie's backing and help from the publishers Walter Blaikie in Edinburgh and Hodder & Stoughton in London), he set up his own imprint in 1926.