Idk if he's cheating?

ok so theirs me and dustin, jess and tina and frazon. jess and tina are sisters. tina likes me but jess hates me because i'm dating dustin who is her ex. so i get a call from a friend saying he thinks dustins cheating on me, but he wanted to confirm it first. so then l8r i get a call from a private number. when i answer a girl says that shes dustins other girlfriends friend. and not much else. so all my friends are bitching at me to breakup with him. so when i called him today, he tells me that jess had gotten onto his myspace and ****** everything up (which is true). when i asked him about the cheating this, he swears to god he's not. so if he's not then jess got my number from her sister tina and had her friend be the one to call me. if he is then i definitly need to end it. what do you guys think is going on, and what should i do?