English Translation
Because I heard his wife is out somewhere.
Although we often drop ”who" if it’s obvious, this sentence shouldn’t. No one can tell whose wife from the Japanese sentence. The English isn’t a complete sentence but a clause. It is likely to be followed by “… he feels lonely” or “… he is relaxed” etc. (i.e. the main implicated subject is “he”, not “his wife”). So, my alternative translation is:
彼は今、奥さんがどこかに出掛けているらしいから。