Dear Striving Catholic,
Thank you for sharing your story. It took a lot of courage, I'm sure.
I was going to reply with some information relating to your original post, but I can imagine that the replies to your story have thrown you into anguish and turmoil.
My advice to you now is to immediately seek the counsel of a traditional Roman Catholic priest. Let him examine your case, and tell you for certain if your previous marriage is valid.
I suggest contacting Immaculate Heart Seminary in Round Top, NY.
Send them a message via email. I find these priests very charitable.
Just Google it, and the website will come up.
A priest's opinion doesn't give you certainty as you suggest, only the Church can give you certainty with a declaration of nullity, which is at present, unfortunately, unavailable.
The SSPV is so indifferentist that it doesn't even require general confessions for people converting from the Novus Ordo. It's useless to gamble on the opinion of some priest and then if one doesn't like that priest's opinion he can go in search of another fallible opinion.Catholic principles in this case are clear-cut and anyone can apply them for himself - unbaptized non-Catholics marry validly when they seek a civil marriage, that's certain, the question is only if that's what happened and StrivingCatholic knows that for himself. In any case, to go seek another marriage a declaration of nullity would be required, which he cannot get, since there is no competent authority to provide it at present.
In short, one can and should seek advice from knowledgeable priests or laymen, however, one can't go seek certainty from a priest's opinion.
P.S. The marriage is assumed valid until proven otherwise beyond any doubt, not the other way around.