Is it normal that he stops before he cums?

Try putting your mouth around it next time... I bet you'll get what you want if you do that ;-)

Coz he feels awkward and doesn't want sticky stuff to go everywhere and for it to be awkward !

It's called edging. He wants you to get him close then stop and build it back up again. Supposedly if you do this a couple of times in a row it's supposed to lead to a more powerful orgasm/ejaculation. It's never worked for me but maybe that's what he's going for.

I don't get it. That wouldn't work for me at all. If she stops, I won't cum. Maybe he doesn't want to? That is weird. I don't get it.

It could be that your style of wanking him does not allow him to Cum?

maybe he likes to wack off later on by himself.

^this. But he should let you finish.