Don't confess. Seriously, NEVER tell a woman you're in love with them until you have them in your arms. It's a horribly bad idea to come on so strong, and it will very likely turn them off to you unless they already feel strongly towards you or are desprate.
If you absolutely feel that you must do this though, don't do it online: you will come off as a spineless, limp dicked coward. Don't do it over the phone, either; it's only slightly less spineless. Face to face is the only acceptable way to do things of this nature.