When you feel that your partner is cheating
What signs do you look for in a long distance relationship when you feel that your partner is cheating?
How are you today?
If you feel him distant, there are good chances that there is something else going on. This something else can be anything: busy with work, a bit stressed up, simply not in the mood for communicating, socially active with other people, etc. Amongst these reasons, yes, there is the possibility that he met someone else. If you want to be sure, here is what you can do:
Ask him, confront him with that.
Listen to your guts.
Check your suspicion. Follow him, spy on him, etc. Very often, suspicions are unfounded. It's a good idea to get your doubts cleared.
Check the facts: how to you come to that conclusion? Are there any real facts or is this just an illusion?
Check with friends you can trust: ask them for their opinion.
Look at him in the eyes. If he is cheating, he'll probably feel guilty about it and avoid looking at you.
Check for unusual behavior, suspect phone calls, sudden plan changes, etc.
No matter what you find out, double and triple check. Don't start building up stories. Try to stick to what you know and are sure about.