You have a point here which could be argued in different ways..If it were to be like what you want, the foundation of the current society would fall apart. If u are not married, u don't have a wife. If you have an offspring, he/she won't have a dad or a mom...lets say he/she does. how about his uncle aunt? and the chain continues...the whole society has been founded on the links of relationship that starts with marriage...

Regarding discrimination based on marital status..hmm...you have a point here..it is more of a legal issue i guess..law only recognizes husband,wife,son,daughter,uncle,aunt..etc....now even domestic partners..but not b.f-g.f.

But i think the moment it starts to, it becomes equivalent to marriage.Once you have a legal tie of relationship, that puts you in the record book..requires your commitment to do so..even you and your g.f now can get married without everyone having to know it..just for legal purposes to avail all that benefits you could reap out of the relationship..

Forming a society is a balancing act..when you balance, you are bound to miss something from the left and some from the right...

Just my 2 cents...