Which Song Contains The Lyrics, 'I Don't Know Why Sometimes I Get Frightened'?

The song you're looking for is probably I Got You by Split Enz. It was the band's biggest hit, and was released in 1980 as a single from the album True Colours.
The song has since been covered and recorded by Vitamin C and The Connells, with artists including Marilyn Manson, Semisonic and Something For Kate playing it live.

Lyrics to I Got You by Split Enz I got you - that's all I want
I won't forget, that's a whole lot
I don't go out, now that you're in
Sometimes we shout , but that's no problem

I don't know why sometimes I get frightened
You can see my eyes, you can tell that I'm not lying

Look at you, you're a pageant
You're everything, that I've imagined
Something's wrong, I feel uneasy
You show me, tell me you're not teasing

I don't know why sometimes I get frightened
You can see my eyes, you can tell that I'm not lying

There's no doubt, not when I'm with you
When I'm without, I stay in my room
Where do you go, I get no answer
You're always out, it gets on my nerves

I don't know why sometimes I get frightened
You can see my eyes you can tell that I'm not lying
I don't know why sometimes I get frightened
You can see my eyes, you can tell that I'm not lying
I don't know why sometimes I get frightened
You can see my eyes, you can tell that I'm not lying