I am looking for a song that have these words in it you can see i the only one who understand you?

The song you are looking for is "The One That You Love" by Air Supply. Here are the lyrics with the part you are looking for in bold:

I want you to know

I'm the one who would give you the strength to go on

When something's wrong

I want to be the one to dry your tears

When they're flowing

In the darkness of your night

I'll be the one to hold you tight

I want you to feel

That I'm the only one who understands you

In every way

I want us to feel that we can stay together

Forever, and ever

And as we drift into the night

We'll feel the peace that we will find

You'll be the one

To lift me up and guide me on my way

When I feel strong

And when I feel alone you will be there

to light my darkness

In the silence of my heart

I'll let you be the one to start