So you can see that plot twist happening like 20 miles away where the guy in the photo with Fiona is gonna end up being some cousin or gay friend who she was with. That kiss was entirely platonic looking.
Besides, this is a girl on Social Media, if he really was her new boyfriend she would have been posting all over the place about it. Not just posting a random pic. So here we see the upcoming "I wasn't cheating but you did you asshole" moment.
The guy who sent the pic to the MC, said "he's in a ton of her photos lately. doesn't look good", so I guess it's on her social media. If you cut every communication with your significant other (we are talking about weeks not a couple of days) and start posting pics with someone else, do you really have to spell it out? Even if she's not cheating, everyone will think see is and since the MC tried to reach her again and again, and she keeps ignoring him, how can she blame him for anything? For me he waited longer than he should.
It's true, it's not a good thing going on. Unless she has a really credible reason as to why she's been radio silent other than "I was mad at you" then yeah it's not justifiable.
If she has time to take pics, real or fake, she has time to send a text... No matter if she's cheating or just being manipulative, everything that happened is on her. She has the typical bitchy behaviour "things should go my way, or else I'll throw a tantrum". I really hope the Devs don't make the MC feel bad for her, if/when she decides to reach out to him. Or at least that we'll get a choice to tell her to fuck off, or get her be the apologetic (I can't think of a better word right now, she should take the blame) one, for her shitty behaviour.