Inlove with my sister's husband

Years ago I dated this bisexual guy and I can pretty much say he is the only person I have ever fallen inlove with. My time with him was amazing until he broke up with me because he said being with another man and settling down with him is not an option(because of the views of society). I took it pretty badly and to be honest I never got over it. Imagine my surprise when he started dating my sister 3 years ago and they got married a year ago. The problem is that I still have extremely strong feelings for him, every time he looks at me I feel like his eyes are burning through my soul, when I see his dreamy beautiful smile I feel like I move to a different world. However he is with my sister now and they are expecting a child. I feel so sad and depressed, I tried dating but I never fit with a guy so well, there is always something I can't come to like or accept in a guy and my depression got stronger and stronger. My sister knows how I feel about it and my mom and dad and even he know too and they are supportive. I thought it would pass but it didn't and 2 months ago the depression and constant sadness grew so bad that I tried to kill myself. I was saved and I have been in therapy ever since but I don't feel any positive change. I listen and try and do everything the therapist says but nothing seems to be working... I don't know what to do anymore. :/