OK let me see. First of all, it would be easier if you had mention if this family member is a male or female, also you could say what it is without going over the edge. Next thing parents are like a sleeping cat, they knew more than they pretend. Most times teenager or some adults when they choose to love someone beyond their family expectation it very hard to say, because they do not want to be judge. This is the same on teenage pregnancy. OK since you do not say much, let me see what i could suggest to you. You may start it like this.
Our roots says we are a family,
but our hearts says we're the same,
and like a palm tree that can be bend through any storm and still stand strong to give shade in times of hot sun rays.
We have all had hard times, yet we stand still.
Now that my own blood has cast a role on me,
From his silent distress, I penned it down with words, thus hoping to relieve all pain.
Bitter tears shed each day, with the many thought that cascade through the mind, represent the unspoken words that are trapped within and the deeds that are left unsaid.
Remember when no scars show, deep inside hide a wounded heal, but digging deep, with open eyes, you can feel the pain that one feels....
and there you can suggest or give a clue of the situation. Hoping this might be of help.