So lately my wife has been working alot of evening shifts, and for the past couple months has been carpooling with a male co-worker. At first I didn't mind, I would rather have someone with her in case she has car trouble or something like that, but it seems that they have become a little bit more than friends. You know the scenario, the phone calls that hangup, she starts wearing nice clothes to work, talking about him all the time, etc. I don't know what to think. If I'm out in the garage when she gets home (usually after midnight) he just drops her off and leaves, but if the lights are off in the garage and I'm in the house (they think I'm sleeping) they sit out in the car for like twenty minutes. I asked her once what they were doing, she said "just talking"....whatever. So last night I decide that I'm going to see what really goes on out there. I leave the garage door open, but turn out all the lights. About the time she usually gets home, I go out and hide in the garage and wait. In a few minutes, his car pulls into my driveway, and I'm hiding behind my bike. When his headlights shine through the garage and onto my bike, I see some thing that I just can't believe. The rear sprocket is already worn and hooked but the chain looks OK. Do you think I should change just the sprocket or the chain and sprocket?