I really like this girl, and I know she likes me, but we have known each other for a couple years and we recently started dating. I want to play my guitar and sing I love you until the end to her, but would this be romantic or stupid and weird. And how and where should I do it, if I do it?

Why don't you wait until your 6 month or 1 year anniversary to do this? It might be too soon to tell her that you love her and it will give you an idea of a theme for the anniversary.

Try singing a more neutral song or a song about feelings without the word love in it. You don't want to scare her away before you even become a couple.

That's a great idea to wait for your anniversary. But if your sure she feels the same way then just plan a special night. Or sometimes the unexpected is the best surprise.

If you have only recently become romantally involved it may be a little early for her with the 'i love yous'.
Even in song.

How about,a romantic dinner,bit of craic,maybe at the end of the evening play something for her,but SLOW down,keep things light and easy going.

I can't stress that enough,even though you know each other for years,this is different...
Treat this like any other relationship at the beginning..

Ahh- I don't want her to go away.. thank you for saving me from myself... I will wait until an anniversary, we have dated for 4 1/2 months, and she says she can see us being together for a really long time. I do I really do love her though, should I do it on the 6 month mark, or year?

I would wait until 1 year, but that's just me.

Do what you feel is right, but 4 1/2 months is not a long time and if you like the way things are going and that she can see you two together for a long time, then why rush?

Depends on HER pace, we don't know her so it's difficult.