Wow, thats a lot of advise requested, but two things jump out,
1- This is not worth ending your life over. There may be some painful times ahead, but removing yourself from the equation leaves more losses than resolutions. Not only does your partner of 8 years lose you, the (potential) child will never know you other than an obituary or news story they find when they dig into the question "who was my Dad".
2 - Go for the paternity test, if the child is yours, then you work out the rest of the plan, but if it is not your child, then you have a better understanding of who you were with. If you are indeed the father, then options can be many, Pay support, adopt with your partner, but be there with the kid if at all possible.