What do you think I should do about this?

I have been in a situation slightly like this, where I feel like there is someone much better for a person than the one they are with right now. The way I see it, if she's happy, and you truly love her, you should be happy to. Would you rather she be happier with the man she met online, or be less happy with you. I'm not trying to put you down at all -- I'm sure you're an amazing person and by the way it sounds I can tell you truly care about her. Let her go though. If she loves you as much as you love her, she'll see it. But there's nothing you can do if she's happier with someone else.