What should I look out for?

Firstly, 17 is too young to be engaged.

Think about your situation now, and how long this kind of thing could go on after you are married before you get really unhappy. A guy who is going to be your husband hiding things from you is seriously bad news. Marriage is based on trust, understanding and mutual respect. If he is too immature to be completely open with you about everything that is going on in his life then you don't want to think about marrying him.

What's the point in holding on with your bloody fingernails? A good marriage should feel like a strong, sturdy rope holding you firmly onto the side of the boat in rough waters. Don't stop looking until you find it.

Well, if you two are the same age (under 18), then he may be curious to know what he may be missing out on because he has been with you. He may want to live a little.

If that is not the case, then you should talk with him about what he wants. Of course if you bring up the emails he will see you as a snoop and try to hide them from you even more. So, you have to have an open conversation about where you two are going in your relationship.

Good luck.