Creating a henchman

I have created an NPC.
I defined all kind of stats.
I put npc and sentinel flags.
By mobprog I make him follow me group with me.
Then we start wandering.
If I attack a neutral mob, my henchman will stop following me and start hitting me.
If an aggressive mob attacks me first, my henchman (again) will stop unfollowing me start hitting me.

Do I miss something?

2 possibilities come to mind:
a) you set the henchmen as helper
b) you didn't have it set itself as charmed when you had it follow you

To charm the hencman means that they players should get
the charm person spell from the start. An if the henchman is charmed, it means that there will be a duration that will be like this.

How i set the henchman as helper?
I dont know this

You need to have a look at the pet functions since what it seems like you're trying to do is reinvent that particular feature.