He has been fighting with you
If he has been fighting nastily with you, then there is a good chance that he will want to move on. Usually, heavy fights will lead by a break up. If you fight, make sure you fight fairly and don’t push it on him and blaming him for everything. If your fight is bad, it could be the reason why he wants to leave.
He can’t stand your personality
If you have ocd, or if you’re a total mean person, he might not be able to stand that. He might be into someone who has a better personality, one where he isn’t bother by it. If you have a problem like smoking, drinking or a habit that annoys him, then he might be looking elsewhere for people who don’t have those characteristics.
He’s not happy
He’s not happy with the relationship, emotionally or physically. He feels that there are better people out there who will make him happier. If he’s not happy, he will leave you.
He found someone new
If he found someone new, he might be dating them. He might be ignoring you because he has found someone new.
He has different goals
If he has a different goal than you in relationship wise, he might be looking elsewhere. If you just want to date but he wants commitment then he might be leaving. If he just wants to date but you want commitment, he might be leaving too.
You’re not giving him what he wants
You’re not giving him what he wants in the relationship. For example, you don’t give him enough space in the relationship or that you don’t give him what he wants in bed. He might be leaving because of these reasons.