I wasn't going to post anything about this because to me it's pretty obvious, but I'm guessing there are many that do not know this so here it goes:
There isn't a woman today in Western culture that will not cheat under the right circumstances. If you are in a relationship with a woman you should always expect that it could happen. It's all about everything really.... nothing happens without MOTIVE and OPPORTUNITY. Granted there are many women that need A LOT of motive, and A LOT of opportunity before they pull that trigger, but it's always possible.
Truth is once she starts cheating, it's not the easiest thing in the world to catch unless you either she consciously or subconsciously wants to be caught. If a chick is determined to no keep this under raps she can and will do this. Her accusing you of cheating.... well, in my experience that doesn't necessarily mean she is cheating... but it is a VERY strong indicator that she is losing interest in you FAST. Why do women do this? Well, it could be she just wants to stir sh1t up... women do that... some just like to see how you will respond to it It will be one of many things she'll say and do to start fights. If she REALLY suspects you of cheating, she isn't going to say anything... she will do some undercover work... dig around... and when she has proof, she'll just spring the trap. If married, you'll find your sh1t on the lawn while you are being served divorce papers. If you are just living with her... she'll just clean you out when you are not around, and she will be gone. If she is your girlfriend, she'll just be gone.
If you are in a relationship with a chick, and you are interested in keeping it going... her active desire and willingness to cheat is just as bad as her actually doing this... because if either of these things happen you are already finished. So what are the signs that she is leaning in this direction?
(1) She becomes distant... she is emotionally distancing herself from you. Don't confuse settling into a long relationship as being emotionally distant. Relationships are not always hot and heavy all the time like the very beginning. But she begins to lose empathy for you, she starts to not give a fvck about your day... she might even get a little mad at you if you start to complain about something... she doesn't want to hear it, because she definitely does not want to start feeling any sympathy for you.
(2) She becomes increasing b1tchy and nagging, which doesn't let up. Everyone has their moments, but when this behavior is chronic, that is when it's a problem.
(3) Observe how her friends treat you... women tell their friends EVERYTHING. If she is cheating, or is thinking of cheating, you can be sure her friends know this. Notice any change in how they behave when they are with you. If her friend actually likes you... you will start to notice this "Oh, you poor thing." demeanor... and if you are really good at reading body language and mannerisms you will get a sense that she REALLY wants to tell you something that will never come out. If her friend doesn't like you, she will avoid you like you have Covid-19.
It's been a long time since I tried to actually make a relationship work, so I do not have any advice for you if this happens, other than to say at some point it's going to be too late to do anything about it. Women and relationships are like water... You start off as HOT steam... eventually this steam cools and turns to water... WATER is where the relationships reside. Relationships condensing into a liquid is normal. But you have once the water cools below 100 C, you have water (Relationship), the 'relationship' is over when it turns to ice 0 C... so you have 100 degrees Celsius where you are with your chick. The closer you get to 0 C, the harder it is to get the temperature back up. So you really have to become a relationship Ninja to gauge what direction you are headed . Now this is where many men fvck up because it is NOT where you are in this continuum, but what direction you are moving and how fast it is going. A chick that is... oh let's say at 50 C, and a dude she thinks is better comes along and shows her some interest... she can go from 50 C to 0 C so fast your head will spin. So you have to notice the little things.