@MercyandFaith you are teasing yourself over an arousing addiction. The more you stoke it and ruminate into it, the less control you will have over yourself and your actions.
First, it is very unwise to be good friends with a married woman (to the extent you start meeting each other's emotional needs) because meeting emotional needs starts building up a love bank account and when it crosses a certain threshold you will be in love (addicted) to the other person. You must wisely stave off an addiction to a married woman before it ever takes hold. Here is a great article about the science behind this concept, written by a Christian psychologist who has decades of experience in helping marriages survive affairs:
Well, it's been my experience counseling thousands of couples that opposite-sex friends pose the greatest risk for infidelity. True, there are those who go shopping for sex on the internet or have one-night stands with total strangers while on a trip. But that's not the typical affair. The most common affair is with someone who has become a friend.
More:
https://www.marriagebuilders.com/are-friends-a-threat-to-your-marriage.htm
Secondly, you should be thankful that you've been exposed to the deceitful nature of this woman before she burned you:
A: She deceived a man into giving her his shot at marriage due to some "circumstances". Her convenience about these "circumstances" was more important to her than honestly letting him know that she preferred another when she married him. This is theft of more than all of his assets and bank accounts, it's theft of his time and the efforts of his heart; it is perhaps one of the most cruel versions of theft out there:
We had liked each other before she got married. But she was pressured by circumstances into marrying someone else, a man she didn't want to marry. And we've still not stopped liking each other. We both regret that she ended up with that other man.
B: You should know that affairages (marriages arising out of an affair) are notoriously unstable and over 95% of them do not last more than two years. This is because the selfishness that allowed the affair in the first place is still present in the second marriage. Do not expect her to have any more integrity with you than marrying you for her convenience (or thrill) but then employing the same cheating/dishonesty towards you. Affairages are notoriously paranoid since both partners know the other has low regard for marriage and will cheat on them.
The actions that will most enable your married girlfriend to have a successful life would be to inform her husband of your mutual feelings for each other and step out of her life so you never see her again. If possible, even move. The reason I suggest going this far is your posts tell us, between the lines, that you are tantalizing yourself with the beginnings of an addiction to her. It's very hard to fight addictions, especially because you instinctively want to nourish and nurse them.
Your doing so will
help both you and this other man's wife have accountability to the person who would be most affected if your addiction survives and will give her marriage the best chance of succeeding.
Sometimes being a man and manning up is hard to do. This is an instance that calls for it.
PS: Don't try to self justify staying in the church and in her circles with the lame excuse about being the church's pianist. The church will adapt and find another option if you leave; the marriage you are transgressing into will not if you stay.