I would suggest keeping your ‘friendship’ a true friendship that a married man could have with an adult female. Loads of other people and activities. No ‘company keeping’, no ‘one on one’ trips or dinners or movie nights.
For instance, my dh can attend parties or business functions without me, but he better not be having dinner with any of the women there to just “talk business” alone. Capiche?
BTW, my pastor during the pre-cana met with my fiance and myself one on one before declaring that the church could marry us. There in the office he asked me, and in turn my soon to be dh, if we were previously married or if we had mental or addiction issues. Or, and I thought this was odd, if I was feeling pressured to get married. (But some people do get pressured, such as the lady you ‘married’.) So, having those issues previously might just be a help in the examination.
Consider having a mass said for the lady you are interested in and your former ‘wife’. Both of these women need prayer.
I will pray for you and your petition. Hopefully it will not be difficult if you really were ‘not validly’ married.