My brothers girlfriend ( may be cheating )

I need advice on what to do . My brother has been dating this girl for over a year now . My brother is such a sweet heart he’s 21 and thus is his first girlfriend . Last week she told him that she may have feelings for this customer at work . Well they work through that and I guess all is fine . Well today I am at work ( we work for the same company) just different stores . I have a coworker come up to me today and tell me that yesterday she drove off in his car ( he left her the keys ) . My thoughts on all of this is I feel like there is so much more going on then she is letting on . This guy is 45 granted she is only 21 and y’all this car was a Tesla !!! A 75,000 dollar car . I mean come on now. People just don’t let anyone drive there car . Especially a car that expensive . Am I over reacting like I am so upset and want to tell him now but want to wait until I see him in person or do y’all think I should just stay out of it ?