So my brother deals pot...?

So my 21 year old brother has always walked all over my mom. He is away at college and she pays his rent car payment EVERYTHING. He hasn't worked the last three years at college and claims to be making money doing so callled odd jobs. Somehow he can afford a brand new mustang. I knew he smoked pot and drank but recently I found out from multiple reliable sources he deals and grows it too. The worst part is that his frat is actually covering the grow op. There are multiple witnesses. He knows my boyfriend of three years (who wears my dads wedding ring as a promise ring) and I smoke once every few months and has tried to rat us out to my mom multiple times. Im 20 have a full time job and was giving my mom loans out of a trust fund from my dad dying so she could help him make ends meet. He brags about making 2000 a week! So he literally has been using my dead dads money I have been saving to get a reliable car and finish college to deal pot. What the hell do I do? I don't know if my mom would even believe me. I thought about leaving an anonymous tip with the citys police department but its a small college town and idk if they'd even do anything plus I don't know if I could deal with knowing I put my own brother in jail. Help??!