Well it is clear that you son is in distress over the failing relationship between you and your spouse. Children are so much more aware of things then we often give them credit for. He is afraid of losing everyone in his life and being left abandoned. You need to be extra sensitive at this time, no yelling or being impatient. As far as his fear at night (ghosts) I know many adults with blatantly dismiss their children's fears, saying 'there are no ghosts sweetie' the truth is, there are....and children are more innocent and have their eyes open to seeing things that we often cannot. Do not dismiss your child's fears, my kids often can see 'the other side' and tell me in explicit detail what they are able to see, and it is often terrifying. Do not ever tell your child that what they are seeing is not real. He probably cannot articulate what he is afraid of, because it is just too overwhelming. Many kids have been told, 'Just go back to bed there is nothing to be afraid of' and their fears are dismissed as being untrue. Don't ever do that. Just comfort him and tell him to say a prayer (or do it with/for him) praying to God for safety, sweet dreams and protection. Let your son stay with you in your room/bed. Realize that his clinginess and tantrums are do to so many things building up in his life - and this is the only way he can cope or express himself, the only control he has left over his life that is changing to something he is not happy with.
Be the mom that supports him 110% and think how things would be if you were in his shoes.