First, under no circumstances should you agree to anything without speaking to a solicitor and, possibly, an accountant or financial advisor,
Now, I am using ball park figures here based on your post.
You put down a deposit of 80k (and lost out on any interest that would have gained if it had been in a bank/other investment) and he is paying off a mortgage of 80k (plus interest because he didn’t have 80k at the time.
Is that right?
Let’s say the house is now worth 300k.
With ring fencing, you get 80k plus 110k (total 190k) and he gets 110k.
Without ring fencing, you each get 150k. What you lose, he gains.
Actually, OP ignore the above. I’ve reread your post and think it is irrelevant.
Your DP is using this as a stick to beat you with. But he signed the agreement, right? In fact, I assume you both did. I also assume you both jointly instructed the solicitor. Therefore it wasn’t a case of you and the solicitor conning him. In fact, if he really thinks that, he (or possibly both of you) need to report the solicitor and seek damages. Im curious as to what his response would be if you said that to him.
He knew what he was getting into because he purposely refused your offer to help pay off the mortgage. He is trying to renege on the contract. I wouldn’t let him. If you stay together, it makes no difference. If you split up, you have just given him a boat load of money.
Given that he is instigating fights over this, I think your long term further is in doubt and would suggest you hang on to as much money as is legally yours as possible because you might need it sooner than you think.