I said no before I read your last line: “or are you 100% truthful about everything with your SO?”
I don’t think anyone is 100% truthful ALL THE TIME, but the only time I will “white lie” to him is if something will hurt his feelings, and even then I try to be truthful. Like the other day he made French toast with nutmeg, and I don’t like nutmeg. He asked me if I liked the French toast, and I said “yes, but I would just prefer it without nutmeg.” So I spared his feelings while getting my point across, so next time, he’ll make mine with cinnamon instead. 🙂
But I feel really guilty about lying, so I think about it a lot. (I used to lie a lot to previous ex’s so I think that’s why. He deserves better from me than what I gave to them.) If there are things I don’t want to do, I just try to be honest. “Sorry, I just really didn’t feel like picking up the cat food. I’m tired.” Or if there’s something (unimportant) that I don’t feel like telling him, I don’t. (I bought three pairs of pants on Monday that I didn’t mention to him. If he asks where I got them, I’ll tell him, but if not, it doesn’t matter.)
It’s the same with others in my life. If my mom gives me leftovers and I forget to eat them, I just can’t bring myself to say, “Yea, mom, they’re gone.” I feel compelled to say, “Sorry, mom, I totally forgot about them. :(”
ETA: I think it helps that my FH doesn’t get mad (and I try very hard not to). We believe that anger is a secondary emotion (that stems from another emotion, like frustration, embarrassment, hurt feelings, etc.), so we try to figure out what the anger is “masking” and go from there. And we are both very good at apologizing when we’re wrong, so on the rare occasion that I tell the truth when I don’t want to and FH says something that I don’t appreciate, he’ll apologize for it (and vice versa).