Like you said, they were transitioning from this fake marriage to real marriage in a very subtle way. A few conversations here and a few revelations there. They had this new found comfort with each other due to the whole Ram being quarantined. That seperation for them and for us, noted that very unknowingly Ram and Priya got used to each other. They missed each other's presence subtly.
Then the whole birthday rough patch and what I believe a bigger misunderstanding than the Shivi and Akki's marriage. I call this bigger because they were the only people involved. Ram had expectations and be felt she didn't care. There was no third party involved at whom he was disappointed for. His whole anger was with Priya. Because he expected her to make him feel special on his birthday. Expectations are always a good thing if they're healthy. Because they show the growing comfort. Again, a very couple like thing to do. He didn't expect anything from the others but he expected it from Priya. That's a landmark.
Rain moment is where I think the gear of their equation changed. They moved from the "we are friends and partners for life" to " Yes, there might be something here between us". We cannot speak much of Priya, because she was drunk and we didn't get a morning after convo. But Ram, he was visibly attracted to Priya. It felt like on his side, the non-platonic aspect of their marriaged got a kick start. It was subtle and not very OTT thank God. Bravo to Disha Parmar though, this is her first work I'm seeing and ghe whoel drunk act was adorably amazing. Nakuul Mehta just endears himself with that stutter and it feels like a very unique trait to Ram.
The negativity and all are omnipresent in TV shows, but what I'm glad for, is the subtlety in RaYa's relationship. There are no OTT accidents, electric sparks and heartbeat raising ( I mean it is in the song, but okay). It's simply two people navigating through life. No villians mindlessly hating the leads. These people hate them because they feel that RaYa's relationship could be a threat to their existence. I find that a completely acceptable villian unlike those villains sans gravitas in our "favourite" show