atsea I know exactly what you mean.
Your DPs ex impact on your life is significant. You can't go away for a weekend, can't tackle DIY together, visits to family are curtailed and simple things, like you never get a lie in together. He can't accept work on a Sunday. It is financially impactive and it eats into your life together. And it's not like it's a temporary thing. Parents of young children know they'll get lie ins again when their DCs are older - but this is (certainly in your mind) a fixed, forevermore arrangement. There's no indication it will change - and it's entirely up to your DPs ex if it does. I was discussing exactly this with DH last night.
But, don't underestimate the impact a family court case will have on you and your DP, either.
A court case is likely to turn your lives upside down for months, if not years, and there is no guarantee that it will change anything. It could drag you into it and you have no recourse to reply. It will cost you, emotionally and financially.
DH decided last year, when his DS refused contact (DSS said it was because it upset his mum) despite a court order, that he would not go back to court for enforcement. Unfortunately, DSS mum applied to court anyway for a no-contact order, to validate her own decision to withhold contact.
There were five hearings over 6 months; DH was ordered to attend the SPIP course (which he'd already done), and I was dragged through the mud in the wishes and feelings report.
We had wanted to avoid all of that - but DH had no choice. He didn't even really challenge his ex's position - merely repeated his position at each hearing, which was that he did not believe that no-contact was in DSS best interests, but he wasn't going to force DSS to see him. Once it goes to court, the origional purpose gets lost and all sorts of peripheral clutter gets dragged in.
And it's made no difference. Contact still only happens when and where DSS mum is happy for it to, otherwise DSS refuses.