Hes having a secret email?

Yesterday night, my partner was using the laptop, after he was done. I went to use it, turned it on, and the website he used popped out. It was mail.com. he usually have gmail, outlook, or yahoo, but ive never seen him using mail.com. i ask him about it and he said its nothing, that he accidently went to that site when he checked his gmail. But i find it unbelievable. On the history, he was in gmail at 6:22pm, but he got on the mail site at 6:35pm. So idk. In the past, he did use fake emails, and create other emails to cheat. But it wasnt w me, it was w his ex. Im just thinking, how he can do it w me too, if hes done it w her. Ive been w him 6yrs, and theres never been a sign of cheating, til now. Or maybe ive missed it. Idk. What do u think? Cheating or no?