He's basically just voicing how every guy feels when a girl takes interest.
He's flattered by your advances, which is normal. Most guys just don't get asked out by girls since we do all the asking, so when girls make a move its a huge ego boost since its such a rare occurrence.
For this same reason, guys typically don't get creeped out like girls do when a person is interested in us and we don't' share the same feelings. The only exception being if we're really repulsed by her or she is coming on way way way too strong.
So basically what this guy is saying is "I don't like you back, but you liking me is cool since it makes me feel good. I'm not creeped out either so don't be ashamed. Please keep on chasing me so I can keep getting an ego boost that us guys normally never get".
My advice is to simply take it to the next level and soon. Ask him to hang out or go on a date. If he refuses you definitely know wherw you stand and you can stop wasting your time flirting with a guy who isn't interested. I would strongly advice you from continuing to do nothing but chat and flirt with this guy online unless you want to risk having your time wasted from nothing.