Maybe we'll find out in the future, but for now i don't think she cheated.
The only thing she found out was that MC and 2nd girl had sex behind her back. As i wrote, she called him right as they were doing it, but the girl picked up his phone and told her what they are doing and then let her listed. She was actually really turned on and masturbated like crazy listening to them.
The hand holding was shortly after this but with the 3rd girl. This was actually just bad timing for her, the 3rd girl and MC were just talking while siting on a bench. I think it was about her love for BL, she had some trauma about it and MC read a BL manga just to support her. She grab his hand just out of excitement for him accepting her fetish. FMC looked kinda flustered and worried but didn't confront them, just turned around and followed her friends. This was the last thing in the latest ch so we don't know her true feelings about any of this yet.
I don't really remember if she felt any disgust, didn't look like it from what i remember. But this is very soon in like 5-6 ch so you won't have to wait to long to get real confirmation. You maybe have a point about her being turned on by that, because of her masturbation i wrote above. She has a very strange fetish from the looks of it, it's not just a normal "i'll sleep with another guy" thing.
I get what you mean. With this one in particular it's the art that got me in the beginning. Now i don't take it serious and just check out the new raw to see how big of a dumpster fire it becomes.