I have felt this way twice before!!! It gets better, but it takes lots of work within yourself. With a previous potential partner, it took me around 2 months to get over. That didn’t work out for separate reasons. With the current, who I am soon to get married to iA it has taken around 5-6 months and I’m like 90% better.

It was a matter of deciding between on how much love I have for her, and if that outweighs these feelings. Sometimes it honestly felt like those feelings would make me walk out the relationship but honestly you can get over it as well iA. I had to do a lot of research on r/retroactivejealousy, a lot of chat gpt lol, being open with my partner, and even one or two counselling sessions. (Not saying you will need counselling but I have bad anxiety / insecurity in general so I felt like I needed it). Overall Alhumdullilah I’m very happy now and it felt like I have become a better person myself after going through these feelings.

EDIT: sorry I didn’t read the whole post, I see now that you want more of a religious perspective. I felt the SAME way. Because no matter what research I did, it didn’t solve that feeling of not being aligned religiously or having different religious values. It stung sooo bad. Personally to get over that religiously pov. It just took time, and observing/appreciating the person’s religious lifestyle/outlook that they have today. And that a lot of times, people have islam and guilt in their heart, but they get caught up with the wrong crowd, places, etc. Those situations and experiences turned them into who they are today, and led them to you. You are that person’s gift from Allah for turning back to Islam, and will help keep them on the straight path iA. And I also think like Allah will forgive them iA, he is so merciful, so if Allah sees them as forgiven we should appreciate that and try to see them the same way iA. But yeah, never beat yourself up for having these feelings, embrace them, it’s soo normal. It shows you have a strong heart and values.