The first thing any behaviourist worth their salt is going to do is check you've seen a vet to rule out medical issues, so that's where you should start.
The next thing they will do is ask you about the dog's life to get an idea of their general wellbeing - this issue aside. This is going to lead back to the walk question, I'm afraid. The good news is that whilst dogs need some physical exercise they are often much more in need of mental stimulation. This does not have to be a walk. Depending on how much interaction you have with the dog now, you may want to change how he spends his days. Expecting a dog to hang around in the house not really doing anything for hours at a time is not fair. As you are at home all day then several short sessions: training, playing, hide and seek with treats etc can really help.
The poop-eating is most likely linked to the anxiety at being left but dogs sometimes do this because they are on a low quality food. Some kibbles (especially) come out almost the same as they went in which leaves the dog nutritionally deficient (dogs sometimes try to gain extra nutrients from poo) and their poop tasting a lot like kibble. It's worth reviewing what you feed the dog to make sure it is as high quality as you can afford. allaboutdogfood.co.uk is great for independent reviews of many of the foods you can buy in the UK so can help you check yours and select a new one, if necessary.
Anxiety when your oh leaves needs to be tackled. It could well be that the changes of you being pregnant has upset the dog to trigger this new behaviour (you smell different, behave different, etc). To desensitize him to your oh leaving the room then he needs to go out/come in often and for very short periods of time.
e.g. He puts his shoes on and leaves the room. You give the dog a treat. Your OH comes back in. Repeat, repeat, repeat. What you are looking for is the dog to come to you as soon as your OH leaves, looking for his treat and not worrying. Then start to stretch how long your OH is out the room for - build the time up slowly.
If the dog cannot even cope with him putting his shoes on without panicking then you need to start smaller - e.g. your oh reaches for his shoes, treat, then lets the shoes go.
In the meantime, I might be tempted NOT to ask the dog to spend the night alone. If he were mine, I would move him into the bedroom to see if that helped. If it did, I would keep him there until he could be left alone again in the day and then work on SLOWLY moving him back out the bedroom to his normal sleeping place.
For clarity: do not add pineapple, do not with hold water, do not withhold food. Unless there is a medical reason the dogs cannot hold pee/poop then none of these is going to help because the cause is behavioural.