I am married twice. Divorced once. and annulled.
Presently, I have been separated for 3 and a half years.
My wife has borderline personality disorder.
I struggle with my circumstance. The first annulment, I relied wholly on faith. The deacon in the archdiocese lied to the archbishop, when I questioned why the deacon told me I should not get an advocate, because if I did so, I must be trying to hide something. Despite being in the midst of the process, I wrote the archbishop. The Archbishop replied that as I had no proof, he could not do anything. My annulment was approved 2-1, and then 3-0 on appeal.
Now I just feel like a failure. My present marriage does not exist in any practical sense, and I do not want to start such a process again. I have no 'love' interest, yet also feel burdened. Why go through divorce and annulment, with so much pain and so little gain, yet what if I encounter a new relationship?
I am a man, 53 years old. I rarely go to mass, which is my fault. I wake with this burden, carry it daily, and sleep uneasily.
Strictly speaking, if your first marriage was deemed null, then your current marriage is still valid. The fact that you are separated really doesn't have anything to do with it. The fact that your wife is borderline personality disorder may make for a crummy marriage (I know this firsthand, myself), but it certainly doesn't automatically nullify it either. So long as your second marriage is deemed valid, you are not available to other women/relationships.
It is a very difficult path. I know a guy who has been in an identical situation as yours for 10+ years (being separated/not divorced/not annulled). It is what it is. Getting a good spiritual adviser and focusing on a strong prayer life is really really really vital. The guy I know became very active with his church and leads an otherwise normal, content life. It is a cross to bear, no doubt, but with fortitude and perseverance, and being open to the graces of Christ, it can be done. Without that, it is very easy simply to give up and fall to temptation.