To tell my 7 year old that his dad doesn’t want to see him…

Word it like some people can't ride bikes., some can't do great sums. Some grown ups can't be good daddy's... I have never had a relationship with my df.. His loss. I have never been arsed. Wasn't because I wasn't good enough.. It was because he wasn't... Don't make it personal saying he doesn't want to see HIM..

Yes - as @Goldbar says always state how much the dad loves them.

And it's true, when a woman gets rid of an abusive partner, when nothing else works the abuser will then hurt their ex-partner through their dc.

Stupid fuckers - in the end they just hurt themselves.

I agree with the male role model thing - do you have any male friends or husbands/partners of your female friends/school mum friends who would take your son out with their children every now and then and give him some attention, praise him, roughhouse with him, that sort of thing?

I would steer clear of saying to a 7 year old that his dad ‘chooses’ not to see him for fear this might crush him.

For now I’d perhaps say something vaguer, like that dad loves him very much but can’t see him as often (but it’s dad’s loss as he’s missing out on such a great son). But there are other dads that see their kids very rarely, e.g. sailors, busy businessmen, or soldiers. So that he doesn’t feel like there is something wrong with him or he is the odd one out.

My mother made it very clear to me when my dad left (I was similar age) that ‘he chose to abandon us’ and I’m afraid it’s scarred me for life. It’s very likely that your son is already struggling with his self-esteem (‘other dads want to see their kids, what’s wrong with me?’ sort of thing) and if you confirm he’s been rejected by his own father, it’s going to hurt him even more.

He will figure it out gradually, as his understanding of the world gets better with age. How he handles it depends on many things.

I’m no expert part from my one-off ‘lived experience’, so perhaps it’s worth speaking to a developmental psychologist just to be sure how to address this?

Also, like someone has already said, any positive male role models would be really beneficial for your son. Even if it’s a teacher or a family friend. Or even a historical figure he can admire. Otherwise he’s likely to go looking for them on his own when he’s a bit older and what he finds might not be so good.

It might be the wrong thing but I would go with something like his dad loves him very much but some people aren't very good at the practical side of being parents - being organised, turning up, remembering important stuff (and you could give him some examples of all the things that parents have to do) and maybe his dad is one of those people.

Oh gosh - I don't know what to suggest. Been through similar myself when ds's mostly absent dad decided he no longer wanted anything to do with ds when he was 12. I think that ultimately I was more upset by the cruelty of it than ds.

Ds is actually fine about it (from every observing person I've asked besides me) the one thing I do not and will not do is slag off his dad to him - no matter what a complete tosser I think he is. Ds is now 22.

When DDs bio dad stopped seeing her, I took the blame. He doesn't like me, he would have to see me, and he doesn't want to.
Then as she got older I told her more of the truth but maintained that I was provably a barrier to his contact with her over telling her that he was a deadbeat who couldn't be bothered.

What I would do, is make time special between you two, discuss things if he wants to, build him up in his confidence, tell him how loved and important he is.
If he continues to feel bad, please seek counselling. DD went over her relationship (or lack of) with her dad in counselling a few years ago, and was helpful

This is hard. I think you need to try and explain it in a way that puts the issue on the dad and not on your son (which it sounds like you're trying to do) but it's not easy!
Perhaps explaining it in a way about how being a parent means doing lots of different jobs - like going to work to earn money, cleaning the house, looking after yourself, looking after children, buying and cooking food etc etc. And that a really hard part of the job of being a parent is finding a way to do all of those different jobs, and that his dad isn't very good at doing that. That way you can sort of explain about the fluctuations ie sometimes he's better at it but he doesn't manage to do it all the time. That's why he lives with you because you're better at fitting in all those different parent jobs.

There might be flaws in that explanation, just thinking out loud but something that takes the emotion out of it a little bit?

Really tough one. Don't have personal experience of this, but possibly look at some play therapy/family therapy to help your son. His school maybe able to support as well - keep them in the loop.
Your son is understandably lashing out at you because he is hurting and you are his safe place to do this. Also wonder what his dad might be saying to him when they do meet.
Are there any other men who he is close to that he could see regularly to have a solid male role model around?
Just keep talking and reassuring him.
Good luck

This sounds really tricky. I would perhaps focus on trying to empathise with his feelings so he feels heard and try not to explain it away as it doesn't sound like there is a good reason? Mental health and financial problems are not a reason to not see your children (unless the MH are severe, which i assume isnt the case?). I think you are right to try and create a schedule, i would keep trying that and dont let ex see them at random times.