In the music video "Who Knew "by the artist P!nk why did she feature the boyfriend as a drug addict?

I believe that song came out in 2008.That same year her husband Carey Hart's 21 year old brother Tony Hart was killed in a motorcycle accident. I can see her writing the song for Tony or even Carey since they were estranged at that time but please what is up with the junkie boyfriend? Thank-you