Partner took a contract that came to my business - now is trying to push me out.

Before I go into this, I understand I made some mistakes with this and did not handle this like I normally do - formally with contracts.

I have my content creation business (Video, photography and graphic design) that I started a while back - and I have a guy I used to work with with at a previous marketing agency that did ads - and he recently acquired that marketing agency as the owner handed it over and left.

We discussed potentially partnering and forming 1 agency, but decided not to do this and agreed to help each other out and white label our services if we had a client that needed ads, and vice versa.

We had a client who we worked with for 3 months, and ended the contract. A few months later they came back (specifically to my business) and wanted to do another 3 months as they liked our work. I asked my ads guy if he was up for it and said yes. This was for content creation and running ads.

The ads guy said he can handle everything, the contract management through his business and we can invoice him for our services. we agreed on a 75% (him) and 25% (me). I asked for a 50/50 split but he said no due to me just doing a little editing. Mistake 1 on my end.

As we have worked together fine in the past, this was just a chat exchange via WhatsApp. No contract. Mistake 2 on my end.

First month was fine. did content and delivered and paid. Month 2 he said there were issues on his end accounts wise, and didn't need anything that month. Month 3 he says my polished content isn't performing, and is heading down the influencer route instead and would like videos adhoc as and when he needs.

I just have a gut feeling he won't be requiring much from me, so he doesn't have to pay my split and can spend that on influencers, and pocket more profit for himself.

The client has no idea this is happening behind the scenes, and whilst the contract is with the Ads guy through his business, the client thinks it's all run through my business.

Now, I understand my bad choices here - but what would you advise me to do? Email the client and relinquish any ties so they're aware my business is no longer involved ad walk away?

Any help is appreciated! (UK based)