Back in May his mum even messaged me inviting me to her 70th birthday dinner, saying that he hasn't met anyone since we split and would I be willing to try again with him!
That's very unfair, inappropriate behaviour in the circumstances.
Is she totally unaware that he's the one who ended the relationship repeatedly and who is ambivalent/vague and totally lacking enthusiasm or certainty about getting back together?
It sounds like he's not honest with her. They certainly don't seem to have decent communication.
On the main topic; you need to have no contact.
In terms of coming to terms with the relationship being over; look at it like this; if you are meant to be together and it's ever "right" from both sides, you'll be together. So no matter what you do, you're not preventing that. He can come back with declarations that he's seen the light and that you're great together and he wants a steady, committed ltr etc ..and you can consider what you want to do (if you're dating someone or not).
I'm afraid if he hasn't been like that in the honeymoon phase of a relationship; he won't; but just reassure yourself that if it's right, you'll both make a definite opportunity to get back together in future.
In the meantime your job is to date and try some other people on for size. You're 100% free to do so. He ended the relationship. You're single.
I predict that you'll get into a relationship sooner or later, and by that time, if he comes back (even if it's more definite than the vague, ambivalent, flaky shit he's been coming back with since the relationship ended) you'll think "oh do eff off mate, not a chance".
You need to build up a similar level of familiarity and time together and history with someone else to put the relationship in context.
Also ... I'm not sure what age you are but just to say, we don't have the relatively unlimited time to have kids that men do. They can afford to mess around for years. We can't. If a family is important to you, you need to prioritise meeting a partner and building a relationship with them towards that aim.