"and is now saying I'm being unreasonable.", this is what they always so. I always throw that back in SO's face.

Your feelings are not unreasonable. Don't let him belittle you just because you don't feel comfortable with him sitting next to BM. I know you can't control him and his actions but try your best to make him see how this makes you feel. Especially the lying.

The issue of trying to control his actions is something you need to think about, I reckon. BUT I would be also totally pissed off with him if he promised he would do one thing and then does another!!!! I get that this must feel like a betrayal since he should not promise it if he doesn't intend to do it. Stupid men- typical stuff- wanting to do whatever is easy for them . He should apologise ! However, the thing itself - to ask him not to sit next or close to her- I find a bit controlling to be honest and I would not like my partner to tell me that either. Of course this is not the point now anymore since he had the chance to tell you he would sit wherever he wants BEFORE he made a promise !!

Really sorry he lied. I get this kind of shit all the time - half truths about stuff that has happened. And this is exactly the sort of stupid ass clown thing my DH would pointlessly lie about.

I think in their heads it goes something like, "it's easier if I lie, because I'll just get grief here for not doing what I said, and it's not a big deal... I was just sitting with her because it was easier than making a point of not doing it, so what's the harm", but like you say the harm is in the lying about it and how that makes you feel, and it is legitimate to get upset about someone lying to you about something - don't let him make you feel that it's you being unreasonable. You sound like there's a history of him lying about stuff? Which I really relate to as this all builds up, so what might seem to others possibly like an over-reaction to one incident is because it isn't just about that one time - it's the lying and the disloyalty when he should be putting your relationship and feelings first - certainly before an "anything for an easy life" approach to dealing with his bitchy ex BM.

I get shaky and cry about this sort of thing too. I would LOVE to do what Sweet Pea says above and waltz in to the next school event. But BM scares the crap out of me! I like playing out that scenario in my head though. I just need to grow a thicker skin.

I don't care about the sitting next to her part, because, hon, you got bigger problems.

I DON'T tolerate lying. White lies, lies to save your ass, broken promises, whatever. I was raised to be honest, DH is always honest (and he knows I can sniff out a lie and fact check like a rabid mongoose), because, if you can lie about one thing, you're likely lying about something else and thus, I can't trust you, and if I can't trust you, then how can I live with you knowing you might stab me in the back at some point?

See, that's what this is to me, an indication of something bigger in the future.

So stupid.

I am so lucky to have a guy who is as honest as the day is long. Seriously. Sometimes I think to myself, "WHY would you even TELL me that?? I don't want to know THAT!!" but then I read posts like this and KNOW that my husband will tell on himself to me just because he wants us to have a 100% honest relationship.

If he'd just told the truth I'm sure this wouldn't be an issue. Lying is way worse than sitting with a BM. What an absolute douchebag he is. Was he trying to just not cause a fight or trying to protect your feelings? If that is the case then lay down the law that you want the truth, even if it hurts and move on from there. Sometimes they are trying to protect us when they are just fecking idiots.

However, if he's a decietful little shitbag then tell him to hit the road...