There is an idiomatic expression in Portuguese:
Onde se ganha o pão não se come a carne
Literally, it would translate to "where one earns their bread one does not eat the meat" and it relates to a common sense advice against trying to woo/seduce/conquer someone whom one meets on a very frequent basis (esp. at the workplace). The closest English equivalent seems to be "don’t get your meat where you get your bread".
Is there an equivalent idiom or perhaps yojijukugo in Japanese for this?