Depression Support Group
Depression is a real and debilitating condition that is often misunderstood by family and friends. Its meaning can range from a prolonged period of sadness to an actual mental illness with specific symptoms. Find and share experiences with others who are going through the same struggles.
You might want to check it out. I am sure that you can do it!
Secondly I also think that doing things for yourself can help you feel better about yourself and help you not think about the negitive thoughts. New haircut, super clean house or car can make you feel good to. Maybe a new outfit. Go sit at the local clothing department store and have one of the make-up girl people do your make-up. Things like that can help jump start your thought process.
I wish you all the luck in your new relationship. bad things happen to all of us, but the bad things are not what defines us.
This may not be overcome with "logic" or "rationality". Seek professional therapy and protect your good fortune. This would probably be very, very good for you in many areas of your life.