Firstly, why were you snooping? Ime people only snoop on their partners when they have reason to be suspicious, and from the sounds of it you have gone to quite some lengths to find out just what information your dh has, what with checking his facebook/checking his mobile phone/matching up numbers/email addresses etc. Why did you have reason to be suspicious? If you can answer that question, then maybe you will be halfway to finding out what is actually going on.
Secondly, I don?t think that exchanging contact details and not telling one?s partner is necessarily suspicious. But I do think that there is a difference between not telling, and deliberately hiding the fact iyswim. I have male friends who have my mobile number/email address, and I have their details. And tbh I don?t know whether I?ve told my dh or not, he does know these friends exist, but I haven?t said to him ?oh, I?ve given x my number? to me that sounds a bit like seaking approval, and I don?t think I should have to do that as they are friends and nothing more. There is nothing on my mobile/in my email account that I wouldn?t want my dh to see, but I would be mortified if I found out he?d been snooping to try and find out who I?d been contacting and what I was saying to them etc, because that would indicate to me that he didn?t trust me, and I would then want to know why.
If you have reason to suspect your dh of something, then I would sit down and talk to him honestly about what is going on, and why you are suspicious. But if you genuinely think that nothing has happened with this girl, then I would let it go. Sometimes we can get jealous with no good reason, but the more we allow the jealousy to take over, the more chance there is of things going horribly wrong.
Oh and I don't think there's anything wrong with having a separate hotmail address to give to people, in fact I think it's very useful to have an address you can give to all and sundry, because it prevents spam coming to your main email address...