Being that your son is only 8, he is still influenced quite a lot by others.
-"I don't have a girlfriend or a social life"
-"My ex started dating this karate master"
If it was your son's choice to see your ex's boyfriend this weekend, it's because he finds him more interesting, and perhaps iconic.
You're ex's current boyfriend provides the portrait of an independent Alpha Male figure who is a karate master, has a girlfriend, and perhaps social life. Children like to tell, and listen to stories. A black belt karate master makes a pretty good story.
Granted you don't have to be in a relationship to "win him back over", but you should consider the following (without taking offence, if any taken... I'm only being analytic here). You mentioned that your boy is going to be a natural Alpha correct? If so, this Karate Master could be very influential on him.
- Be Interesting (We've all been bored children at some point in time. On those boring days, what did you WISH your parents would do with you? Go for a random bike ride? Theme park? Movie Theater? Play at the park?).
- Following the first jot... Put yourself in your son's shoes (What am I doing with Karate Master? What is Dad doing with me? What sorts of activities appeal the most to me? One of my single parents now has a boyfriend who is a Karate Master, cool!)
- If he's drawn toward the Alpha Male icon, you'll have to show that you're Alpha.
- I'd suggest to dlv certain aspects of Karate Master, that you don't want your son to inherit. Don't be direct about it. For example, don't say, "It sounds really stupid when that Karate Guy starts yelling". Find some random stranger who is yelling, and then say "wow, he's going to have NO friends yelling like that...". depending on how similar the situation is, and how memorable you've made it (by using expression), your son WILL remember what you said the next time Karate Master goes to yell something at someone.
(You'll only be able to do this once you've proven your Alpha to your son, dhv yourself, and "Be Interesting", as pointed in the first jot.)
- DO NOT MAKE ANY ATTEMPTS AT BRIBERY. Bribery will only show you're weak, if your son catches on that you're letting him do this or that IF he stays with you for the weekend, then he'll begin to like you for all the wrong reasons.
*Expect something like this with any new boyfriend your ex might be in a relationship with. It's the adolescent curiosity, interest, and (perhaps) iconic Alpha portrait, that is luring your son to this Karate Master.
*Also expect that this may all change with time, as your boy throws away his adolescent tendencies and see's more admiration for the laid back father who has raised, and has always been there for him.
He's an eight year old child, so certain aspects of the game WILL work. What we're working with here are..
- Building Interest
- Demonstrations of Higher Value (Toward You)
- Demonstrations of Lower Value (Indirectly Toward Karate Master)