Could He Be Cheating?

Yesterday I noticed a visible stain on the passenger seat of my husband's car. I questioned him about it and he said that it had been there for a while, which is untrue because I only just noticed it. I brushed it off and didn't press the subject any further.

But then lastnight I got to thinking and remembered that there had been a few times in the past few months that I had gotten into his car, the passenger seat, and found that the seat was reclined. I'd ask him about it and he'd always say that I was the last person that sat there.

Now I don't want to jump to any conclusions, but it definitely has me concerned that my husband may be having an affair. What do you all think?