Do I just run from this mess?

[Brixtonrunner]

Tell me what to bloody do wise mumsnetters because I don't trust my judgement anymore.
Six year on/off relationship. Off because he would refuse to talk about next steps for us or moving in, I'd get frustrated, call it a day but we'd somehow get back in touch and on it went. We're mid 40's, I have one DC he has none and was a confirmed batchelor before we met. He confessed recently to sleeping with someone last Nov when we were 'on a break'. Said it was a one time only thing, he felt horrible, he felt ashamed of himself afterwards and that it was because he was so lonely and upset that we weren't talking.
Since sharing this he's talked about finding a place together, future planning, all the things I'd wished he'd been open to years ago. I was naturally upset but then was able to reason that it was while we were on a break and we weren't speaking so he was free to do whatever he wanted. A bit of hysterical bonding later and I'm feeling rubbish about it. Not least because the woman he slept with was a former colleague who'd been in a junior position in the team he headed up at a former org. They'd stayed in touch, she'd invited him over to a party one Sat night and they'd took it from there. And he hadn't chosen to tell me till months later when I pushed him to share if he'd had any involvement with anyone else while we were on breaks. I love him, I'm sure he loves me but there's a nagging feeling now that he's just a bit of a dirtbag. Do I let bygones be bygones and seize on his newfound desire to settle down? We get on so well when we're together, have same interests and aside from romance and an end to loneliness, I'd massively benefit from sharing household costs (romantic I know but I'm also practical 😁).
Or do I run with that nagging feeling and bring a six year struggle to a close and try to move on? Is he to be trusted? Help!!

He didn't do anything wrong.
It's down to you whether you can let it go or not, because it wouldn't be fair to bring it up in future.
What's your gut say?

Why were you so nosy and intrusive about his personal life when you weren't together? Who he was with is none of your business. You're both waving red flags honestly.

You've given it 6 years. There's a reason it's been on off. Face facts. It won't ever be fully on. Cut your losses and run.

I think the sleeping with a former colleague is neither here nor there if you weren't together.

But 6 years on and off, it's time to let it go. If you were 25, I might see how maybe he's ready to grow up and knows what he wants. But at mid 40s, with no serious long term relationships prior to that, I don't think things are going to change.

Six years? Have some respect for yourself. He’s just not that into you and is using you for sex and company when he feels like it. Don’t waste anymore of your life on this guy.

I’m always wary of anyone in their 40s who has never settled down at all.

He’s a complete waste of time which you’ve had to endure for a long six years.

This will be yet another ‘on’ stage until things don’t move forward again, with the addition of you feeling the way you do about him sleeping with someone else. Talk is cheap.

Do yourself a favour and move on.

agree with others, its time to move on, you've wasted 6 years with him and you are no further forward. . i wouldn't waste another minute on him, he's never going to commit.

Cut him loose. He's doing the cycle of abuse with you. On, off, on, off, on, off for SIX years. Even if you buy together I doubt he will be fully emotionally committed to you but he will have found himself a willing housekeeper.

there's a nagging feeling now that he's just a bit of a dirtbag

Do you think that this is how people feel about each other in a healthy relationship, @Brixtonrunner ?

You've given it 6 years. There's a reason it's been on off. Face facts. It won't ever be fully on. Cut your losses and run.

This ^^

Don't be a fool and get entangled buying a house or sharing a mortgage with him.

He's been flaky for 6 years. What more do you want to know?

He won't lead you to a path of happiness OP.

I have one DC .

As a solo mum, I'd say concentrate on them. You don't get a second chance to do right by your child.

Men come, men go, but a child is for ever.

Just sometimes you need some tough talking from strangers on the internet who can cut through the crap and provide an objective perspective about your situation. Thank you to all who responded.
The clear theme is not that he slept with someone else but that we're stuck in a crappy cycle which shows no sign of abating until one of us has the guts to pull the plug. And this has to be me. Eurghhh! I'm too old to have allowed myself to get entangled in this. What a waste!
To the OP who said put my dc first. You're absolutely right, everything I do I think of her needs and because she gets on so well with him and he invests time and effort into the stuff she's interested in I thought it would be an added bonus having him around permenantly. But he's a manchild and it would be another six years and we'd still be where we are now.
Thanks again all for some straight talking sense. Massively appreciate it!

I'm too old to have allowed myself to get entangled in this. What a waste

Stop with the self criticism. You've stayed because you're a decent person who has tried to forgive. All you've done is be nice. No need for a bunch of self blame here. You've realised, and you're moving on. Bravo.