You wont. You can either give ur trust until proven otherwise...or break it off. Long distance never usually works out anyways besides a realationship wont work if you dont have trust communication friendshp and of course respect and love.
Hmm long distance.. Look for the signs if you truly know your partner then it should not be hard to figure out if he's acting strangely out of character. And sorry but in my opinion Long distance relationships never work.
is he reducing his time calling you or in webcam or whatever means of communicating? If yes and he says due to work, start getting fishy. I'm in this line (how to get a girl to like you that sort of expertise) and I say use your gut feeling. A girl's gut feeling is 90% bulls-eye! my web blog for guys at http://seducingbeautifulwomen.blogspot.com.
Listen to your gut! If you suspect he is, then you're probably right. Unexplained periods of time when he's unavailable, postponed visits, secretive emails or phone messages, the list goes on and on. Without trust, there is no relationship! Long distance relationships are difficult even for the most committed, trusting people. If you're not happy, then definitely re think this relationship!
My ex of 3 1/2 yrs had been cheating on me and I found out by going there on a surprise visit. I had the keys to his house and just went there to surprise him for his birthday but on an earlier date. That is the best way to figure if he is cheating by going to his place and seeing if your belongings or pictures are present or if there is someone else's belongings there. Yes, I too agree on postposed visits, long periods of time before you talk, gut feeling of you feeling like a vacation buddy with benefits and apologizing for things that didn't need to be sorry for (such as using a past tense rather than present in a sentence) WTF.