So basically, I believe that another person should never be your main reason for such an adjustment. You have to come to a realization within yourself that the change would really be better for YOU, whether or not you are dating and wanting to please someone else.
Totally agree. My initial response to the OP was run, RUN,
RUN!! If someones foremost desire to change is for the happiness they percieve they'll attain by being with someone else, when they get that person, (and realise how human they are) and have achieved 'the goal' - the incentive to stay that way can lessen and the person can backslide. The pressure of being different without the true internal changes that only God can bring will eventually crack the temporary facade and it'll come down. That can be pretty devestating for the person who's believed in them.
Someone has to change because they want it for them. Because that's the only way they'll have enough steam to keep pursuing it permanently until they get there. Anything else is like uncomfortable 'dressed up' clothes for church. Restrictive. Polite. Create a great image but you can't live in them.
People who live with abusive partners or addicts face this same cycle. The person they love really 'wants' to change and often trys hard, usually at least several times if not many. But eventually they go back to their old habits because changing 'for' someone else just isn't enough incentive to keep going. It has to come from within them
for them. And at a pace they can cope with and maintain.
We can all want to be a better person for someone we percieve as better then ourselves, and if that only takes a bit more effort (because we've been slack but are capable of it) then it's doable. But when the gap is too large that change is based on a mistaken premise and can devestate the innocent party when it falls through. We can't be someone we're not. No matter how hard we try, the best any of us can do is create a good facade. Who we are is who we are and that's just the way it is.
So if it was me (from what you've described) I think I'd be running!
(pray for the guy, but beyond that, if he's not in your league, just let him know kindly and move on if the whole situation is in terms of a relationship. To make him think he's got a chance will just cause him more pain (or you both if you go out with him) and then you'll be guilty in the whole thing as well.
My thoughts from what you've posted anyway.
Hope that helps. (Sometimes the worst thing we can do when we care about someone is sell out - and that works both ways.)