Yikes, this sounds, really complicated.
I get that it’s hot to be told not to cum but I’d worry that your dom is putting this rule in place in order to undermine your relationship with your husband, so I’d be very careful with this.
I think you probably need to revisit this with your dom and question whether it’s appropriate him creating rules that affect your sex life with your husband. If hubby was into it, then that’d be great, but I suspect it goes beyond ‘no interest’ to him having at least some hidden resentment about it, and so you’ll get more and more passive aggressive shit if this continues.
If you really feel it’s all okay, and want to keep the two sides mixing as you are, well the obvious answer is get hubby to fuck your ass more, plus get better at just focusing on pleasing him, get him to cum with oral and handjobs so that he’s sated and you’re just left horny and desperate.
But be smart, take a little step back and think about what’s really going on here with these two guys, and be brave and talk to them honestly about the situation – in any relationship, communication is vital. When it’s an open relationship it’s even MORE important.