They both have scars, physical ones from bullet wounds and emotional ones from… well, from life taking every opportunity to kick them in the teeth.
Lost loves, parental neglect, imprisonment; few people come to Torchwood undamaged and they’re no exception.
It takes almost dying to make Owen notice Tosh, see her clearly for the first time. And just as he starts to consider a relationship with her, she almost dies at Gray’s hands. Saving her life cements the bond between them.
At night they trace each other’s scars tenderly.
Without them, they might not be where they are now. Together.