There are signs that you can tell your girlfriend’s cheating on you:
Less physical, sexual, and emotional contact with you;
Spends more time on her phone, texting;
Goes out a lot, wearing makeup and sexy stuff;
Cannot be reached out sometimes or always;
Acts panic when you’re close to her phone especially when the phone is unlocked;
Refuses to let you see her phone;
Claims to be texting with friends or business when you ask her who she is texting to;
Etc..
To find out more signs, you can read here: Signs of a cheating girlfriend.