Dear Michael,

Thanks for the question.  

Technically you are still married, even for the Church, and an annulment can't be investigated until such a time as you are legally divorced; hence your conundrum.  

I would say that if you feel that you have real grounds for an annulment, which is essentially saying that there was a real impediment to a sacramental marriage from the beginning, i.e., lack of true freedom, improper ceremony, etc., then, by all means, proceed with filing for divorce.  Infidelity by itself is not the basis for an annulment, though it may be symptomatic of an invalid marriage.  

Marriage is forever, and an annulment basically attests to a flaw that prevented a sacrament from being valid, so it is not a "Catholic divorce" but a recognition that God never ratified the union because of some impediment.  To understand more of this distinction, it would be good to talk to a priest and to sort out the rest of this equation.

My gut is that if you do not feel you need to find another relationship, just let it roll.  

God certainly wants you to be happy, but he also wants you to be heroic in virtue and honor vows inasmuch as you can.  

Taking care of your estranged wife is not an unworthy goal, though the world would scoff at that.  Individual freedom and personal fulfillment rule the American ethos, but God transcends culture.  He speaks to our conscience.  

So pray and seek the Lord in determining your path.

Peace,