Our hearts have a way of naturally defending themselves when they have been hurt in the past. Its just a natural defence....if you stick your finger in a fire and get burned, your going to shy away from doing it again. Its just a natural defense.
Heart break can be very traumatic for anyone.......more so for men then women sometimes because men take a little longer to really fall for someone then women do.
As for working it out with anyone, the fact is you likely have just not met anyone that sparks something in you yet. Most people get discouraged when they do not find that spark again quickly and assume that they never will. The reality is once you have loved someone deeply its harder to stick it out and give it time with someone new. Your not feeling that spark right away and giving up to easily.
A real relationship is built on more then just that spark.......the love you had with your ex was real love. You spent time working on it, these new relationships you are not investing as much because you are afraid of love.
The key is to go with it..........if you are trying to hard to find it then you will pass it by every time. Get out and meet people, date other women and find things in common. If you are questioning every feeling then it is not going to come naturally and you will feel numb to it all.
Stop questioning and just start living........