People move out of relationships or look out of relationships only when they require something they aren't getting. In very few cases is the person you're in a relationship with is a loser you can't make things work with. You chose that person because you believed you could make things work with this person. So deal with it instead of running from it. Make it work.
It may feel very unpleasant when your partner steps out but then why don't you just communicate what he needs so badly? Talk. Communicate.
It happens all the time. Sometimes people want more admiration. Sometimes they want more space. Sometimes they are just lost and need you to help them find a way. Sometimes all they need is a hug. If your partner needs something, provide it. Find out what they need. Be interested. Thats what makes you partners.
If things seem less than perfect, make them perfect. Its not all that difficult. Do something beautiful for your partner. Make them feel special. Give them a reason to stay and you'll find that they would never want to leave.
