My girlfriend (27f) is upset with me (29m) for letting me ex (25f) ride on the back of my motorcycle

My girlfriend (27f) is upset with me (29m) for letting me ex (25f) ride on the back of my motorcycle. I dated my ex about 4 years ago for a little over 6 months, after we broke up we stayed friends because she’s in our friend group (she’s my close friends cousin). I’ve been dating my current girlfriend for about 8 months. Last spring I got a motorcycle and ever since the motorcycle my ex has been begging for a ride because she’d never been on a motorcycle. So last week I finally gave in and took her for a ride. Nothing happened, we’re just friends. But my girlfriend got super upset saying it’s basically cheating and that my ex wants me back etc... how should I handle this?