Love is exactly what the difference between a friendship and a relationship is. Think about it, if physical attraction was the only difference, what does that say about asexual people? Can they never be in relationships because they have no interest in sex? What about people who are somehow unable or simply don't want to? I know of a man who had an accident and can no longer have sex, but that doesn't automatically mean he is no longer in a relationship with his wife. There are a great many couples who are celibate by choice or necessity who still share a deep love with their partners.
Furthermore, you're making some pretty big assumptions. The difference between my boyfriend and my other online friends is that we're actually planning a future together. We can actually see ourselves getting married and even plan some of the details of it. We've discussed children and our views on various important things which we will have to deal with later in life. There is a kind of depth of affection that is profoundly different from any other kind of platonic relationship. If you have not experienced the feeling of loving someone else than that is probably why you can't imagine an online relationship working out.
And let me clarify what I mean by love. I don't mean the hot-headed emotional feelings which people often mistake for love. I'm talking about the very quiet subtle kind of love which is, first and foremost, a choice to love perfect someone who is by nature imperfect. That means choosing to overlook their faults, seeking their good over your own, and shutting your mouth rather than saying something hurtful in the heat of an argument. Many people misunderstand love such that they "fall" for someone easily, invest their hearts and get them broken when they discover they weren't really that keen on the person anyway. For a good long while, I was in love with the idea of love, with the idea of having a boyfriend rather than with my boyfriend himself. I took a good year before I was able to assure myself that, yes, I have taken off my rose-tinted glasses, glimpsed his ugly sides and still love him in spite of those things, and that is a choice, not some wishy-washy feeling.
So yes, there is a big difference between friendship and a relationship, and contrary to your beliefs, it is not sex.
To the people who say "I don't think they can work out but I've seen some of them work out", what you really should say is "I don't think it could work for me." Which is true, because a lot of people wouldn't be able to cope with the distance. It takes a really strong connection to last for any length of time and two mature people who're not slaves to their sex drives to make it work. If you wouldn't be able to do it, that's your position on the matter, but please don't just declare online relationships as completely and utterly unsuccessful 100% of te time, you're committing a fallacy of logic, and I am living proof of that.
You're talking about an online relationship while he's pretty much talking about "can a relationship exist without sex?" and obviously thinks no sex means no relationship.
Though that means, by his own definition, that he's probably never had a relationship