Cheating man? Ringworm/jock itch on hand?

I have a sneaking suspicion he is cheating on me. There was one other occasion where he had ringworm on his hand in the same spot. It was months prior to this. I also found a garage door clicker in his car. He claims it belonged to the previous owner of the car and even emailed this person in what I felt was an attempt to cover his rear end. Why did I have to ask him to do that? Why would he leave someone else's garage door clicker in his car? Why not just throw it out? Mind you it was hidden in the ashtray which I'm sure the previous owner cleaned out. Quite sure actually. It's a pretty non descript item so I feel that the owner who told us to just throw it out could have thought he left it in the car but hadn't. Why so long after we got the car was this a topic? My SO has been really distant toward me as well as disinterested in sex. He picks fights with me or all out avoids me. He's also started paying closer attention to his appearance. I just feel something is going on. Even though I confront him about why it logically makes no sense whatsoever that he'd hold onto someone's garage door clicker for a couple of months without thinking to notify them or just throwing it out. Why would he only do that at my suggestion? Also, the ringworm on his right hand which has now spread to his left hand grosses me out. I'm very confused and need some advice/thoughts on this.