There are no photographs or tapes of Chris cheating on Gwyneth. Without any evidence of him cheating, one cannot accuse him of adultery. However, there is a photograph of Gwyneth kissing another man. The couple did not openly disclose any adultery committed by either spouse. They simply announced their separation.
I don't believe that Chris Martin has cheated on Gwyneth Paltrow. For starters, as I obviously don't know either of them personally, it would be wrong of my to speculate on exactly what has ended their marriage, but sometimes, these things just happen. People fall in and out of love all the time, and there's just as much likelihood of this happening to celebrities as anyone else. They are both busy with their respective careers, and from all news reports I've seen, they tried to make it work, and they just couldn't.
No, Chris Martin did not cheat on Gwyneth Paltrow. Ms. Paltrow said nothing to indicate that the demise of her relationship with Mr. Martin had anything to do with cheating. Rather, the relationship came to its natural end, and that end was mutually agreed to by both Ms. Paltrow and Mr. Martin.
We are living in a world where people are getting cheated on all day long and have to deal with their personal lives, that is their business, they will handle it eventually, whether he did or not. If he did it was not right, he need to do his dirt alone, and not bring anyone else down with him. My advice is if you like drama and nonsense then be that stick in the mud by yourself. And if he didn't then great they can go on with their lives.