Feeling like there is no hope.

I do not know how to post on these things, but I am giving it a shot (and hoping it works). After an hour of crying and feeling down, I decided to make this account hoping to gain some support and just people to talk too. I am currently a mother of a wonderful 2 year old and 6 months pregnant with a second. Very unplanned and surprised bundle of joy. The catch is that I am in a very big bind. I was with my most recent ex for 2 years prior to this pregnancy, and during the month of concieving, I made the mistake of having a one night stand while we had an argument. There is a very short time spand between the two and I am needing a DNA test to determine the paternity. (Please do not judge.) Well, my ex is being very supportive but distant due to the fact she may not be his. The "one night stand" has denied any fact of it possibily being his. This is where I am devistated. I have a two year old, I am 21 years old and barely making ends meet from being a single parent to my first born. She's the light of my eye and I would do anything for her. I am no perfect parent but I am the best I can be. I have dicussed the DNA testing with my ex and he was agreed if it his he will take joint custody and help support her every way possible to ease the stress of having two children. But, if the baby is indeed the other guy's I was thinking of letting two wonderful people that I know and love dearly, adopt her. They're unable to have any more children and have been looking to adopt a child. I know they would love her more than anything and they have what I do not have to support her in life. But, I can't imagine giving up my first born and I feel like this means I do not love my second. I am very depressed and upset whenever I think about this may being the outcome after giving birth. I do not want to be selfish keeping her knowing I will not be able to fully give her or provide for her all she needs. I just don't want people to think down of me by "giving her up". I love this child inside me, more than anything. And I know when I look into her eyes I will see my daughter, my light, my everything. But, I also know the adoptive parents will love her just as much as I. Is there anyone here who has been in the same situation or here to give me advice for birth parents during pregnancy? I would really appreciate anything. Thank you!