With Heart Problems all but gone for good, this VN has to be the best currently out there. This is my first check-in since the last update and it's good to hear progress is being made.
As for those finding issues with Chris, specifically in terms of believability, I assure you "friends" like him exist in every friend group once an attractive woman is thrown into the mix.
I have a couple IRL stories (neither involve me directly) that I eventually want to turn into a VN and one of them involves a very similar situation to this. My cousin's friend's were trying to fuck his GF (now wife) for years. A few didn't even try to hide it and actively worked to make it happen. Guys will always try to get pussy and it takes a rare, rare friend to not go that route.
As for Anna's believability, on the unfaithful route you have to have it be in her all along. Yes, she could have denied Chris immediately but then the unfaithful route is tied 100% to blackmail/r*pe. Which, blackmail can be hot if written well but I think it's more believable if there is at most light coersion with her being open to it (even subconsciously) due to her relationship falling apart by whatever means.
As someone wrote above, relationships often come apart due to basic things like communication, stubbornness and volatile assumptions. Again, I know people that ended years-long (5-10yrs+) relationships for reasons neither could fully define or explain. A lack of communication ended it or drove one of them to another person.
Relationships are strange sometimes. I ruined the one I cared about most for reasons I cannot fully explain to this day.
