How do I know if my boyfriend cheating?

[Mariyah]

He has a younger sister my age, and She is friends with his ex-girlfriend, Rayanne.
I absolutely hate this girl. She always spends the night at his house with his sister. But, her Facebook status always will say something like "Is it odd if your ex likes gripping your hair?" Or "I love when my ex never leaves me alone." Also, He is constantly rude to her when hes with me or her friends. But, from what I hear from his cousins, his sister, and The stupid bitch Rayanne, hes nice to her when their alone.

[Jeannie]

Ex-GF is instigating with those statuses. And BF is a two face. Dump him or talk it out, no lies.

Hard to say if he is cheating. How does he behave around just you?

[Torch-Bearer]

Simple.
Don't allow him to visit you only when he chooses and when he leaves.
Confront him with his cousins. Let him see you in the company of his cousins.
Watch his reactions. Deliberately open R..in the Presence of his cousins.
You can trap him and enjoy and make him leave you on his own.

[Spar Ticus]

maybe the cousins and sister like her more than you (hell you said the sister was friends with her), and they know she gets under your skin... by planting seeds of doubt, they are helping you get rid of him so he can go back to her... and those status updates, are just helping those seeds grow