Even though to some people marriage is thought to be the only legal connection between man and woman -I do not see it that way . To most medieval authorities, a girl friend [concubine ]- is permitted. That includes the Rosh, Raavad, Ramban/Nahmanidess and others that I have forgotten off hand. Even to the Rambam/Maimonides there is no prohibition involved except for lack of doing kidushin [marriage]. That is,- he sees the kidushin as an obligation, but lack of it is not a prohibition in itself. And not all versions of the Rambam have that either. [''Rambam'' is said with emphasis on the first syllable. ''Ramban'' with emphasis on the last syllable ]

Besides that, a girl friend relationship is well established  even after the giving on Mount Sinai of the Torah as we see in Chronicles I chapter 2 verse 46 concerning the concubines of Caleb ben Yefuna. [That is the same Caleb who was a friend of Joshua. See whole incident in the Book of Numbers. Joshua and Caleb were among the 12 spies that Moses sent into the Land of Canaan [Israel] and they brought back a good report as opposed to the other ten spies]

[And even if you find a good woman, she can leave any time she gets tired of you and your beer cans on the couch, and take the kids and half of anything you own, and she will get paid by the government to do so.  Who needs it? ]