Even if you assume that everything the person has told you is true, and every picture is actually them, and you've talked on the phone, and even video-chatted, I don't personally believe someone can really be in a romantic relationship (meaning a "more than just platonic friends" relationship) without having met in person. I think there are certain aspects that are not measurable or quantifiable about how we as human beings behave, act, smell, touch each other (or don't touch each other), the little ticks we do that we don't even notice, etc. that play too large a role in who a person truly is, to make it possible for that romance to truly develop without meeting in person.

I do think people can become emotionally invested, and even love someone, and friendship in this way I think is totally possible. But I don't think you can fall IN love, or have a more-than-platonic relationship with someone you've never met. There are aspects of a romantic life partner that are different than friendship aspects (and I don't mean sex), that I just can't be explored via other means of communication...these are the things that we just can't put into words.
"I don't know! I don't know why I did it, I don't know why I enjoyed it, and I don't know why I'll do it again!" -BART SIMPSON