Your legal advisers should have got this right. If you are applying for a fiancé visa, the critical evidence is proof that a ceremony is going to take place. If that evidence was not included, UKBA won't have bothered looking at anything else. Your legal adviser should know this.
There is nothing to stop you preparing for the wedding by making provisional bookings for almost everything and submitting evidence of those bookings and providing receipts for things that you have already bought such as rings. If you don't have any of this, it would be most unusual.
Add to this the fact that you are considerably older than him, he has previously failed an attempt to remain in the UK and subsequently been removed, and yes, it will look suspiciously like the primary reason for him wanting to return to the UK is not because there is a genuine ongoing relationship.
UKBA and the law does not care about your heart. You have to provide the cold, hard evidence that you are a genuine couple and meet EVERY requirement.
I suggest you put a rocket up your legal adviser as clearly mistakes have been made in their advice to you if they allowed you to apply without any proof of a planned ceremony; that's sloppy. Take the emotion out of your reasoning and try to see it from UKBA's point of view and you will see much more clearly what you both need to do to meet the requirements at appeal.
You will not change their decision by pleading, declaring undying love or talk of shattered hearts. The law has no emotions or empathy. You must argue using facts and evidence.