I remember that stress! we printed the handbook off and put it in a folder and then worked through it one section at a time, i.e found all the finance evidence, social evidence, statements from friends ect. doing it one step at a time and breaking it down makes it so much more managable. and don't be affraid to call up the embassy to ask for any help they are fantastic.
for evidence of on going relationship and living together don't forget your council tax bills, car insurance ( if your named drivers) recipiets paid for by the other i.e i damaged my car and my husband paid for it. once you start looking you will find lots of evidence- just break it down into managable steps.