Difficulty: Moderately Easy
Step1
The first thing you notice if your mate starts not answering his/her phone in front of you. That's a definite sign he/she has something or someone to hide.
Step2
Your mate gets extra flashy on a regular day for example usually your mate wears jeans and sweats they spiffy it up a notch or two.
Step3
Knowing you and your mate hasn't had sex they don't want to is a sure way to know they are seeing someone else. also recognize a different smell on your mate