I've been with my current partner for ten years. For the first six months, I went through the same surreal routines as before with him. Then I thought, "To hell with this! He's a kind man, he'll understand." And I "came out" to him about the parcopresis. It wasn't easy. I explained that I'd HUGELY appreciate it if he could wait for me outside, say, if we were going out for the day, or take a turn round the block sometimes. He thought it was silly, but he IS a kind man and he does it. Sometimes he's exasperated at being asked to "go for a little walk" when it's pouring with rain - and I don't blame him.
This has made a massive difference both to my life, and our relationship. Yes, it helps that we don't live together (and of course, my parcopresis is one of many reasons for that). But he could easily have told me not to be so stupid, "grow up" or some such, and refused to support me, and I'd have either made myself ill, or ended the relationship.
Now, we can even laugh about it. I will adopt a strained expression and he'll sigh and say "You want me to go for a stroll?" I know I don't have to invent more lies and go through absurd charades, or worry myself sick - literally - about it.
All of which is leading up to saying, to anyone in a relationship where you haven't been open about your parcopresis, please do consider it.