What to do if you suspect someone on friends list of boosting/cheating?

Pretty sure my buddy being boosted. I realize a lot of people being boosted this season so its sad to see. I see he has been playing with the same people the last few games, which I pretty much can guarantee are diamond/plat smurfs. I realize this is legal but I am also pretty sure he has someone playing on his account as well. No idea why you would have someone play on your account and then also play with a premade but that's what it looks like to me.

He's currently on a 17-1 streak and although I am pretty sure 6-7 of those games were him I can't imagine the last 11 or so are. He literally never plays adc and 10 of the last 11 were all played as adc. Champions I didn't even know he owns. He even has a game played with legit cs & /k/d/a and she is not exactly that easy to just jump into playing. He was also on two accounts at the same time last night one in ranked and the other in aram which pretty much confirms to me he is not the one playing on his account.

I have mixed feelings because even though its my buddy, I don't condone cheating. Assuming he does have someone using his account other than himself I really hope the account gets banned. No reason he deserves to reach gold or higher ranks until he legit gets better at the game and can do it himself.

Any suggestions?