So the first question that needs answering is: Is an online relationship different to an offline relationship?
I want to begin with a quote from a Psychologist (bear with me it's a relevant quote):
“As much as I respect and enjoy cyberspace relationships, I would be very unhappy if I could ONLY relate to my family and closest friends via the Internet, even if sophisticated visual/auditory technology made it seem like actually being there with them. Cyberspace relating is a wonderful supplement to IPR [Inter Personal Relationships], but in the long run it's not ultimately fulfilling as a substitute, especially when it comes to our most intimate relationships. Most people who develop close friendships and romances in cyberspace eventually want and need to meet their friend or lover in-person. And once they've done that, returning to cyberspace-relating can feel at least a tiny bit flat and incomplete, despite the effects of the online disinhibition effect.”
http://www-usr.rider.edu/~suler/psycyber/showdown.html
No matter how much we try to avoid the issue it will seem obvious to anyone who has an online and an offline relationship will know that there is a major difference between them.
Will this change with improvements in technology? Some of this will change because one of the intentions of those developing technology for the Internet is to improve the ability of people to interact online. Virtual worlds that we can physically step into are on the way but ultimately they will always be virtual and this will never change.
Most online relationships at present are text based. They revolve around email, chat rooms, social networking sites, bulletin boards (forums), etc. Despite the use of some strange text speak for certain things that people may experience in an offline relationship (e.g. LOL = laugh out loud, or [[Chris]] = hugs for Chris) there is a major difference between experiencing them and writing about them (I find LOL an annoying bit of text speak myself whereas a friend actually laughing - especially at my own jokes - can be delightful). Anyone who has ever had an email misinterpreted will understand well the difficulties in getting a point across, especially a humorous one, in writing. Modern web tools are allowing more interaction between people as they write online and it is true that interaction is one of the elements that is important with any relationship. However I think we are just deluding ourselves if we believe that this is anywhere close to talking with someone where they are physically present.
What about those online interactions that are not text based (e.g. video conferencing, 3D environments, etc)? Well, it is certainly true that being able to see/hear someone when relating to them gives us an added level of intimacy. The ability to hear someone's voice and see their facial expressions is a big bonus but it is still not the same as meeting with someone. I speak with my parents on the telephone but it is not the same as meeting up with them (as they like to remind me from time to time). Of course being present in a 3D form is possible online but this is still a very long way from the kind of relationship you might have with a person in the physical world.
Online relationships also tend to be much safer than those offline. It is easy to form a relationship online and then later to find another person you would rather spend some time with and just to ignore the original person. This happens so often that most of us don't even realise that it is happening (until you think that you haven't had a message from them for a long time). This does happen in the offline world but only where people are far enough apart to allow it, when you are meeting people regularly you are forced into managing your relationship with them (I would hope that no one would be rude and try to ignore them - although even if you did you are still manageing that relationship, only very badly).
One of the other issues is that people who are online often assume a different persona than they are forced to wear offline. Somehow being physically present forces us to be more honest about who we are (I know that people still lie about themselves offline but somehow it is easier to pick this up when you are physically present with someone than when you are not). There have been tragic consequences to this at times where people have lured unsuspecting victims into a meeting after online interaction where they pretended to be someone else). This is also born out by web sites like 2nd life that are keen to promote the idea that you can have another life online and create a new person for you to inhabit (anyone want to be a dragon?). Counter to this is the argument that people will open up online in ways they never would offline. People online tend to be much freer with what they believe and are generally more rude to others. This could suggest that for some their online personality is actually more real than their offline. Of course this is impossible to prove one way or another.
I think that the only response must give is that online relationships are different to offline relationships. There is something about being physically present with another person that you just can't replicate online.
Of course this does fit in with the Christian concept of who a person is. We believe that God created a physical world for us to live in. The ability to interact with that physical world is important for people. God created more than one person because it was important for people to have physical companions (I'm not talking about sex – by the way). We may be spiritual but we are also physical and the spiritual cannot be simply taken out of the physical (at least not until death – or maybe not even then). It seems to me that to deny the difference is to deny part of God's purpose in creation.