Sorry to hear that, OP.
It looks like there's an onion ring.
Partners should trust each other and shouldn't be controlling.
But look at the next layer - the lie about spending the day and then the camping trip with that colleague. And that colleague who has criticised you and he's not been sensitive to your feelings nor, it seems, stood up for you with his mother and this woman.
Ultimatums aren't great but what would the alternative be here? Reminding him he can treat you like this. I doubt it will get better with this colleague, other situations or his mother. You're doubting yourself too which isn't great.
If you're a trainee solicitor then think about a negotiation with a counter-party. Don't let him shape the narrative or frame things so you are in the wrong.
See what he decides to do about the camping trip (no one needs to go on a camping trip with colleagues, especially that colleague) and don't fold or you will have a lifetime of feeling worse than this.
If you stay with him, you might need to give some thought to managing your in-laws so he has your back. It won't get better if you want children and are more dependent on him financially, especially if the MIL sees you as a money-grabber. PMSL at the credit card jibe.
By the way, he should want to spend time with you on a day off if it suits, not consider going fishing with a colleague.
If you marry, I suspect at best, you'll have a bumpy ride with your DP who doesn't seem sensitive to your feelings and in laws. At worst, he is or will be having a fling with this woman or the next.
Good luck.