MAHAL usage if it means LOVE

Examples:

I love you. = Mahal kita.
I love you so much. = Mahal na mahal kita.
I love you too. = Mahal din kita.
I love him/her. = Mahal ko siya.
I love you all. = Mahal ko kayong lahat.
He/she loves you. = Mahal ka niya.
They love you. = Mahal ka nila.
Do you love me? = Mahal mo ba ako?
Do you love him/her? = Mahal mo ba siya?

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MAHAL usage if use as a term of endearment.
Mahal is also used as a term of endearment like love, honey, sweetheart, babe, etc.

Examples:
Love, have you eaten already? = Mahal, kumain ka na ba? 
I miss you, Love. = Miss kita, mahal.
Take care, Love. = Ingat ka, mahal.

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MAHAL usage if it means EXPENSIVE

Examples:
That's expensive. = Mahal yan.
So expensive = Sobrang mahal
This is an expensive watch. = Ito ay mahal na relo.
It's expensive but durable. = Mahal yan pero matibay.