How long into the relationship with your SO did you realize that you were in love with him/her? I don’t remember, precisely - but maybe two months
When did you first tell your SO that you love him/her? Five months
Ever said it too soon/ think saying it messed up a relationship? No
Regret saying it? Never
No offense taken. Since this relationship started two years ago, I’ve had to come up with ways to explain it, not only to friends and family but myself as well. (And for what it’s worth, my SO is 29, and I will be too next weekend.)
In the case of relationships like these, you need to discard the idea that there is one way people fall in love-- that is, by meeting in person, talking a lot, and then falling in love. That first step gets pushed to the end. Which is no big deal, because assuming the people involved are being honest and sincere, there’s no reason two people can’t fall in love without ever seeing each other in person.
The assumption of honesty and sincerity is a big deal, though, and it should never be assumed that the person you’re involved with is presenting themselves as they really are. But it’s up to the people involved to develop their own bullshit detectors. Trust has to be built. In my case, in addition to conversations my SO and I had, I took a look at how he treated other people, and how other people treated him. I got to be friends with his real-life friends, and met them in person last year. Nothing I observed or heard about him contradicted with the mental construct I had of my SO, and that added to my trust in him.
The online aspect aside, our relationship isn’t very different from relationships we’ve had that started face-to-face. How did we start talking? By seeing that we had common interests. (We met playing a MMORPG and chose names from the same fantasy book series.) How did we get to know each other? By talking a lot-- making jokes, talking about our lives, talking about ourselves. How did we develop feelings for each other? By liking the person we were getting to know. How do we sustain the relationship? By doing the things anyone does to sustain any romantic relationship.
You said that one way you know you’re in love with someone is by seeing them and feeling the spark of physical attraction. I agree, and it’s one reason I’m dying to meet him in a few weeks. But physical attraction, IMO, feeds infatuation more than it does love. I don’t mean that physical attraction is unnecessary-- it’s definitely important to be physically attracted to your SO. It just isn’t a strong indicator of love to me. I’ve had some pretty shallow relationships where physical attration was clearly there.
If my boy and I meet and there’s no spark there, then at least we tried. Two years ago, we knew we’d be jumping into a long-distance online relationship. We decided to go for it anyway. We figured at worst, we’d have a great friendship and the memory of a very sweet romance. That’s a lot better than what other people are left with.
None of this is to say you have to give your friend your blessing. In fact, I think you should help him keep his feet on the ground, and encourage him to carefully think through what he’s getting himself into. Don’t rain on his parade or anything 
but try to keep him from getting carried away.
How long into the relationship with your SO did you realize that you were in love with him/her?
We met online - on here in fact!. He emailed me on the Friday, we knew we were in love by the Monday - 3 days later.
Don’t ask me how I knew, but I knew and it was different from the other time I thought I knew. Totally, vastly, completely and utterly different. It is entirely possible to fall in love with someone without meeting them; in fact, I asked him to marry me before we even met. We met in person two weeks after the initial email and there was absolutely no going back LOL!
When did you first tell your SO that you love him/her?
On the Monday - so 3 days after we intially emailed.
Ever said it too soon/ think saying it messed up a relationship?
No
Regret saying it?
To a previous boyfriend yes, in hindsight because now I know it wasn’t true.
As to your concern regarding your friend, trust him to know his own feelings. If he crashes and burns, be there for him but you never know, this could be the best thing that ever happened in his life. It is possible to fall in love without meeting the other person, I did and we’re celebrating our 2nd wedding anniversary next Monday.
So if there’s no physical spark, is the romance over? Would you continue believing you were in love with him if you had no attraction for him whatsoever? Could you continue to have this long-distance thing if you had no desire to be with him as a lover?
- About a week after we became a couple. But we’d known each other for years.
- Two weeks in. After he said it first.
- Nope
- Nope
I should clarify that we exchanged pictures early in the relationship, so it’s no mystery to us what the other looks like. I can safely say we find each other attractive. 
My answer to all your questions is that I won’t know for sure until after we meet. I could guess that yes, it would end the romance, and no, I couldn’t continue if there was no chemistry. Chemistry and attraction are vital to romance. But we’ve been happy for 2 years despite the strains of distance, and I think it’s unlikely that a(n initial) lack of chemistry would automatically break us up.
We’re not very worried. For us, the hurdle isn’t whether we’ll have any chemistry, but whether we’ll be able to wrap our brains around the fact that we’re standing together in the same time zone, state, zip code, 10-foot radius, etc. We both think we’ll be fine once we overcome our initial shyness.