Jenna, I don't think you're suicidal. Yes you have a fear of heights, and probably quite a vivid imagination, especially because of your friend. I find sometimes when I'm standing somewhere really high, I wonder what it would be like to jump, then my head spins a bit, and I push the thought out of my mind and hold onto anything nearby tightly. I'm not suicidal.
Still, it would be worth mentioning to your therapist. Perhaps you need to talk through the loss of your friend. Must have been traumatic for you.