Evidence both ways--is he or isn't he?

My husband and I have had a pretty good relationship for 8 years, but I've been suspicious on and off. There have seemed to sometimes been odd things that neither of us can explain.

The positive--he always comes home right after work, he never texts anyone I don't know, I've never found anything on his phone. Never found anything on his computer, either. Doesn't go out by himself, doesn't extend errands.

The negative--he took many days off last year due to mental illness (yes, I believe this is true), but I wonder if a few of those days, he had someone over. There was a big circle of what I believe was a lube stain at the foot of our bed, though at first I thought it was oil. He said he didn't know what it was. Whether it was lube or oil, surely he must know how it got there? One of us should know. Perhaps most compellingly, every couple months for the past two years, his mouth has smelled like pussy. He was able to convince me he just scratched himself and touched his mouth (those two smells can seem kind of similar). But we moved recently, and there has been no smell in almost 5 months. Which tells me...maybe there was someone, or some two/three at our old place? And he hasn't done it here because...he hasn't had the opportunity.

Tell me what you think, is he cheating or isn't he?