Laughs, pathetic.
I can and will tell you straight away and honestly, LoveLost. I'm assuming she's Christian, most likely protestant. I'm religious myself, so I'm confident I can guide you.
Depression is common, and it disables you, so increase endorphines. Excercise until you sweat, a lot of healthy food fruits, and in extreme cases, masturbate (the brain will secrete endorphines) but WITHOUT thinking about S or else it's futile. Yes, I'll repeat what everyone here said already, erase everything about her.
Now, about J, she does all that for you because of her religion. I can tell she's a true rare jewel among religous people. But kindness will not change into desire just like that. You're truly being pathetic if you let yourself act as in a rebound. (meaning you're dumped and you take the nearest comfortable person around to have sex or to be sexually attracted.) If you can't let go of "S" then give it up cuz a relationship based on pity is !@#$%$#^[insert 5-word long blasphemy], and is destructive for both.
You should face her honestly, and not say "I had an urgent matter and couldn't go to the date". Sometimes "doing my best" is not a good mindset. Neither is the "regret is worse than rejection" attitude. Be focused and clearly think your moves. Practice your lines if necessary in front of the mirror.
Chances like these are nothing but miraculous. So be focused.
Ok, now be vocal about what she does to you. She knows she's helping you, but it has to come from your own lips. Tell her you are thankful blah blah that she's helping you with your problems. [add anything you want here and keep the flattery going]
BREATHE DEEPLY, pause, then look at her and give her a (shy) smile. Then give her unique compliments.
You, being too straightforward with her will only turn her off. Don't expose your feelings for her verbally (they obviously show.). Let her kindness take over the best of her, and ask her for next dates. You'll know when she breaks in and make the "official move".
Alternatively, you can hypnotize her into having sex with you but there's no relationship in that.