why is love so painful

I loved you,
You said that you loved me too,
and I believed you but you lied why?

I gave you so many chances,
but you screwed me up.
Every chance I gave you why?

I thought to myself,
Every time before giving you another chance,
If you cheated on me several times, why not again?

But I was so weak...
Because you always said that you would change,
Just to make me happy.

When I had the strength to leave you,
You came running to me with your warm hugs,

and your sweet lips.

Making me weak to let you come back to me why?
I want to know one thing why is love so painful?