Is it possible to fall in love over the Internet? I don’t think so. It is certainly possible to find someone special, become very interested in them and grow attached to each other, but you don’t know whether your relationship is going to work until you meet in person. There are cases when people finally meet, and something doesn’t “click.” It happens; there is just no chemistry. For that reason, I would recommend to guard your heart and not to think in terms of “being in love” before you have met, not to mention making marriage proposals and getting engaged. You might feel very strongly that you have found the right person, but until you have met and spent some time together, you cannot vouch for anything. Your meeting is the final test. Do not rush into it, but do not postpone it indefinitely, either. If you meet prematurely, it might feel like a date with a stranger, and if you delay it too long you might develop the habit of having this virtual friend in your life. This is not fair to the other person.
Of course, there are circumstances beyond our control that may force us to postpone the meeting. My future husband and I had first planned to meet for Christmas, then it had turned out that he could not make it. My next vacation was only available in May, so we waited till then. If you have valid reasons for a delay, there is nothing wrong with it. The other person will understand, and it will only strengthen your relationship.
And the last thing: what to do if you meet, and there is no chemistry? I would say give yourself some time to get over it and move on. It is a sad situation, especially when one person does feel the attraction and wants to continue the relationship, but the other does not. Just like with “regular dating,” be honest, and do your best to part as friends. You might decide to continue to remain penpals for a while, or you might feel that it is better to stop writing altogether.