Help with a poop fear lol

So I've been with my husband for 15 years. FIFTEEN. and I have never once pooped around him (where he would've known) he jokes with everyone how he's never "caught me" pooping but it's actually a mental problem as stupid as that sounds. We have 3 kids together, which makes this almost crazier. You would think by NOW I would be comfortable enough, but I'm just not. I also have a fear of pooping in public (my body literally shuts it off and I just can't, as much as I NEED to.) This happens when my husband is home as well, my body shuts that switch off until he leaves or is completely preoccupied with other things where he won't notice if I disappear to poop.

So obvious problem is, I end up getting sick. Just a very "full" feeling and nauseous, because I can't get it out when my body needs me to. This past weekend we only had our youngest, the other 2 were with grandparents. My husband was so excited because this obviously means it's that much easier to be intimate but I was SO sick I just couldn't and I couldn't get the guts to just tell him what the problem was. He was very clingy because, well, we were 2 kids less. He wouldn't leave me alone to where I would have been comfortable enough to just GO. This is a big problem and I'm not sure what to do about this. Ugh.