Why are guys considered jerks when they stand up for themselves?

Why are guys considered jerks when they grow a backbone and won't play along with a womens mind games? I broke up with a girl that was playing WAY too many head games (mind games) so I found another girl who was really nice, sweet and REALLY attractive so I went with her. Now my ex is calling me a jerk?! Why? Because I refused to play her games? Thats not nice...so why are guys considered jerks when they finally stand up for themselves. Help me out here.