How can u tell if your gf is cheating on you?

I am so confused and and idk wat to do. How would I beable to notice if she's cheating or nt?How can u tell if your gf is cheating on you?
pay attention to how she reacts when you talk about your future or how much you love her and how much she means to you. if it is anything but a genuine smile, start to worry. another tip: check her phone. when someone txts her, reach for her phone...if she doesnt want you to have it she's most likely hiding something!How can u tell if your gf is cheating on you?
YOU LOOK AT HOW SHE HAS CHANGED IF YOU HAVE BEEN DATEING HER FOR A YEAR AND SHE WAS CONSISTENT IN THE THINGS SHE DOES AND THEN ALL OF A SUDDEN SHE START CHANGEING HER WAYS LIKE PICKING A FUSS ALL THE TIME OR BUILDING A CASE FOR NO REASON OR PUSHING YOU AWAY MORE THA USUAL ON A GOOD DAY JUST THINK ABOUT HOW SHE USED TO ACT TO HOW SHE NOW ACTS AND IF U NOTICE A BIG DIFFERENCE YOU MIGHT WANNA CONSIDER THE FACT THAT SHE IS CHEATING
Maybe if she starts walking funny.
Ask her. It's the only and best way if you are unsure.