It is only sinning if you don't get an annulment first
I should know, I am unfortunately in that situation (annulment obtained from diocese but no solemnization of civil marriage yet). Needless to say I am in a state of sin and barred from communion until the Catholic marriage happens.
Sorry to say, but
1) I would never talk that lightly about "getting" an annulment. A faithful Roman Catholic who thinks his previous marriage was invalidly administered (because one of the partners had incurred or practiced one of the marriage defects) will only ask for the diocese or archdiocese or jurisdiction to start a process researching his or her marriage and the validity thereof.
2) If you already knew that you were not yet validly married, and you were a Catholic (bound by the canonical form), why would you then yet commit the grave sin of concubinating (and presumingly fornicating) and write about it here so lightly. I think you are way too liberal on these isss. A marriage does not "happen", it is planned. And as much as I sympathize with you and know how love (and - let's be honest - sexual attraction) can overtake and dominate your personal actions and mind, I still cannot understand why one would peril his/her eternal salvation despite knowing (and believing - as a Catholic) things and the situations are wrong and gravely (possibly mortally) sinful. Why would one like to live on the edge of the abyss called hell. It is not like you or I know when we are going to die. Memento mori
and carpe diem
inspirational mottos, and contrary to popular thought, are intrinsically linked and not mutually exclusive. Would I live in sin, I would not be able to be happy, pray, be in harmony with God, family, environment, friends, world and fatherland, and not enjoy life.
I hope you will quickly get your marriage fixed and that you may develop sincere contrition and receive valid absolution in the most holy and precious Sacrament of Confession and Penance.