Frankly, I don't see the purpose in checking text messages or the email of someone you love (or following them for that matter).
What are you looking for? What will you do with the anything you find? What good will come of it?
Whenever I hear a story like this from Facebook, online or word of mouth, it never ends in a good way. Because checking someone's text messages starts from place of negativity, namely suspicion and distrust, you'll end up in a place of negativity.
That means if you check the messages and find out the love of your life has in fact been unfaithful to the relationship, you'll be hurt. With that hurt you will be angry and you will want a confrontation in which case you will need to admit you checked the text messages. So now you've been unfaithful too. Did you find what you were looking for? Does it help your relationship? Will it help make your relation healthier and better balanced?
On the other hand if you check the text messages and find out there is nothing out of the ordinary about the text messages; maybe the after hours text messages were related to a special work project, or maybe a friend was going through a crisis and asked it be kept discreet, or maybe the love of your life has decided to cut phone cost and stop sending you so many text messages. The point is you checked the text messages and didn't find anything unfaithful. However, now you must deal with your conscience and the consequences. This can mean you will keep the act of distrust to yourself, which will inevitably eat at you until it does cause problems in the relationship. Or if you decide to tell the person that you checked their text messages that too will cause problems in the relationship because it says you don't trust the love of your life. And a relationship without trust - its a relationship in trouble.
So again I ask, what good will come to the relationship if you check text messages of the person you say you love?
Because if your answer for checking someone's text messages is to say you want to know who and why... then the best approach to take is the most direct approach: simply ask!
Communicate; because that's the way to cultivate and keep a healthy and balanced relationship.