For nobility to be able to marry for love is almost unheard of. It can happen but the majority of the time love is the lowest importance to factor into marriages. Marriages, for nobility, are about political gains and similar such things. So, this has lead to the development of Consorts, which all the kingdoms accept as allowable, who are the 'love spouses' of nobility. The Consorts are considered equal grounds as the married spouse, by some nobles even more important because when they take a Consort it is for love with no political gains factored in, at all. While the Consort doesn't take the name of the noble they are a Consort of (or vica versa) they are, in the eyes of the citizens of Atharia, married to that person, just like someone who is arranged to marry for politics and joins the family. A Consort is often treated on par with the noble they are a consort too. Though, they aren't given the title. A noble that is a consort would still be called by their appropriate title along with the form address for Consorts. So it would be like, assuming a noblewoman, 'Lady Treasured <name>' while the commoner would be called 'Treasured <name>'.
Not all of nobility has to, some don't even want too, take a consort. No one can have more than 1 Consort, not even royalty. Commoners are even rarer to take a Consort since they don't have to worry as much about political gains. So, sometimes it is possible for a commoner not to understand that nobility considers a Consort very important. Commoners marry for love and politics, nobles marry for politics. The commoners who might take a Consort are Bishops/Bishopesses and above of the clergy, Baronets, Sages, Knights, and Matchmakers.
All Consorts will have to form a contract with the noble they join with, just like it were a political marriage. Since nothing political needs to be worked into their contracts they are far less complex. The only 'complex' part would be which family the children would join, as in which family name they would take. When it is a noble or royal and commoner Consort relationship, it is not always directly sorted out in the contract because they often wait to decide until they learn if the child remembers their past lives or not. Though, when it is the case that has titled nobles involved it is understood that the child will not inherit unless the marriage spouse can not have a child. After all, the political marriages are typically done so that a certain family can claim the title to be in their line. There can be other circumstances where a Consort's child can inherit but the lack of heir is the main one. People become Consorts out of love and devotion, so they aren't concerned, save for the more conniving types who think it could happen, about children inheriting and the political gains they get from the match. A note, unlike political marriages, Consort contracts are known by the couple involved and the clergy member witnessing the contract and MAYBE the family head should they need to know, as it is view as something very intimate due to it being about love and not politics. It is /always/ written into the contract that the Consort is given a living/expenses allowance, with more added should children be born from the union.