If you pass that, after date number five, the issue of kissing and intimacy begins to come up, along with the boundaries and interests. If there isn't a deal-breaker, then you will get into more dating and a comfortable routine. You need to be cautious. You don't want your heart hurt again, so don't give it out so freely. Millions and millions of women enjoy oral sex, but they are concerned about scents, cleanliness, germs, etc.
Some people consider it to be more intimate than intercourse.
It could be a measure of their insecurity. It is a great thing to do because you have much more control over your tongue than you have over your penis. In an online affair, it is such a new territory that we don't know what it means. If there was no physical contact, then this could have just been a fantasy adventure. If they did meet and have phone conversations, that is a little worse.