Hi swise -
First of all, STOP right now and call a priest you know and trust and schedule an appointment to meet with him to discuss the situation. Bring as many of your marriage and church documents (for both your and your husband) as you have readily available. Only a priest, canon lawyer, or tribunal representative should be advising you on this matter.
OK? Now - continue reading.
I was in exactly this position when I began thinking about joing the Roman Catholic church. At first I decided that it was just too much trouble to go through the annulment process, too painful. But after about a year of going to church and adoration, my husband finally suggested we take baby steps and see what happened. We both made a pact that if things began to be too much for either of us, we would halt the process.
At first things looked very grim, but after hours and hours of adoration and prayer the situation unfolded like a rose in June . . . and far better than I would have ever imagined. My husband and his first wife had a peaceful, heart-felt, conversation that could have only been under the guidance of the Holy Spirit. And my husband was granted the annulment about a week later. And two weeks after the annulment was final I was accepted into the church, my marriage was convalidated, I was Confirmed, and received my first Holy Communion. Less than a year later - on Saturday night’s Easter Vigil - my husband was accepted into the church, was Confirmed, and I administered his first Holy Communion at my first Mass as an Extraordinary Minister of Holy Communion.
Amazing things can happen when intention meets prayer and adoration!
What if my husband hadn’t been granted an annulment? Well, as I understand it, I might still have been able to enter the church, but I would not have been able to receive any sacraments. For us, the brother - sister living situation thing is out of the question. This is where expert advice is needed. (WARNING: Not all priests or nuns are knowledgable about canon law as it applies to marriages and annulments. There is a lot of bad advice floating around and if you have to take the extra time to find an expert, do so. It will save you a lot of grief in the long run.)
You will be in my prayers -