My Best Friend thinks I'm hitting on his Girlfriend... PLEASE Help Me, I'm Flippin Out.....?

Ok, so I have TWO best friends... One is a dude, who's name is Chuck and we met in Elementary. we're about to go to college and room in the same school. The OTHER is a chick and her name is Veronica. And i Love Her, She is Like my Little Sister! Really, we're close, but only like brother/sister. Thats All. And Chuck and Veronica are actually going out. But thats where the problem is. i usually hang out with both of them. but Lately whenever Chuck is doing something and leaves Veronica alone, i just hang out with her. but Chuck thinks I'm HITTING on her. so he wont talk to me now. and im like "WTF!" he KNOWS i would NEVER do sh!t like that to him ever. i mean after ALL this time does he REALLY think i would do that to him. and i dont even SEE Veronica that way, she's just like my sister thats IT! so now hes pissed off at me, and ive got no idea what to do. ANYBODY.. Please help me... what should i do??