You can't. That's why there is what we call trust.
get a new boyfriend
get another boyfriend and make ur ex boyfriend jelous
When he is your EX-boyfriend and you are over the relationship. Let your heart be your guide.
Forget HIM!!!! Go out and find you another guy to date! Act like you don't care, that will drive him nuts! My personal opinion is that you can do much better!
If your boyfriend starts to stop showing affection towards you and is always busy and going out instead of being with you. These are signs of your boyfriend cheating on you.
Everyone forgets something, usually because the mind is occupied by another thought so you tend to forget
For going to another country
Forget about it. You are not going to like everyone in your life, but you need to be polite and respectful. She could become your mother-in law.
there might be one
See if he flirts with another girl, or if there are rumors going round about him fancying another person, ask him about it!
Of course he is going to be mad
You can tell if she is really destined to leave him if she moves on by opting for another boyfriend.