I think that was after his first wife died. I do wonder to what extent his later somewhat casual sex attitude was influenced by the traumatic experience of his first deep love dying young.
My understanding is that this attitude predated Arlene's death. In his writings (I think it was What do you care what other people think?), he noted that someone told him Arlene (his then-girlfriend) was 'running around' with other guys. It was an attempt to make him jealous, but he noted that he was dating other girls, so it was only fair. (My phrasing, not his.)
It very much sounded like they were both comfortable with their relationship. Granted, this was his writing many years after the fact.
I don't think the claims that he was a womanizer are relevant or fair. People say that kind of shit about MLK to discredit him. Similar claims against Feynman don't discount his love for his wife.
