Like your other concern with your application, it depends on your level of risk-aversion. From the advice I've seen on this board, having the £437.45/mo extra after rent/tax/utilities puts your application in the "likely to succeed" pile, rather than the "possible rejection" pile.
So if he pays £500/mo in rent, and 1/3 of utilities each month (I'm just going to make up £50/mo for that, since you didn't list a figure), and you add in the £437.45, his income would need to be at least £987.45/mo. If it's only £800/mo, you will risk refusal, if only because if he's supporting you, his bills will go up (you'll be buying more food, using more water/electricity, etc.)...that is why there is the recommendation of the £100.95/wk on top of rent/tax/bills, because that will cover the expenses you will add to the household.
If you plan on getting a job once you're there, you can attach your CV and a list of jobs that meet your qualifications to prove that you are highly likely to get a job, if that is the case (I don't know what you do for a living or what the job market for that field might be). I don't think this will dramatically help your case, though, unless you have a job offer in hand (since anyone could claim that they'd be eligible for that £80,000/yr job based on their skills, but that doesn't mean they would be hired to do it).
If you prefer the advice of the immigration adviser to what I've just listed (which is what I've gleaned from reading similar questions/answers on here), that's fine, but that's all the information that I can give you. (Other posters may provide more/different information, of course.)
Edited to note that I forgot to include council tax in my above numbers, but I think it's rather a moot point anyway.