First, I'm sorry you are having such a hard time. Second, I think
makes some really good points and I hope you will consider them. Third, I'm not sure what kind of input you're looking for exactly so please disregard what I have to say if it is not helpful.
I am not in your situation, but I have had some similar experiences that may allow me to understand a bit. When I got pregnant with my daughter I was using birth control pills and had recently changed prescriptions. I put any symptoms down to my body adjusting and didn't realize I was pregnant until 12-13 weeks. DH (then BF) and I only began dating about 6 weeks before she was conceived! We were not overjoyed, and that's an understatement. I've learned since then that it is very common for women who are recently pregnant, even ones who were trying to conceive, to feel unhappy about the pregnancy. Or a host of other feelings besides the cultural script of blinding happiness. For the most part it seems that these feelings fade, or are dealt with adequately, by the time baby arrives. It's still worth checking in with your care provider about though, and talking to a counselor or trusted mentor.
About 6 years ago (when DD was four years old) I was single, working and going to school full time. I kept getting sick and was having horrible headaches. It turns out I have MS and my vision has been deteriorating since then. I can no longer drive safely or read comfortably (sometimes if the print is large enough I can). It is obviously not the same as what you're dealing with, but I do have experience parenting with (and without) visual disability. There are challenges you will face that other parents don't, but overall I think parenting will be totally doable and not substantially harder for you than a sighted person. Parenting is hard for everyone.
You are right that you will no longer be able to live your life just the way you have been. But if I may be blunt without being rude, you are wrong that you will not be able to do the things you want to do or enjoy any of the same activities you do now. I was kind of a wreck in some ways, but at my sickest I was still able to parent my daughter singlehanded and have something of a life. (not gonna lie, it was really effing hard) If I can do that, you can parent through whatever difficulties your circumstances present you with should you choose to do so. Now I am a stay-at-home-mom of two with a caring partner. There are things I can't do at all, or can't do alone. Most of the things that are important to me I find a way to do. I take the kids out by myself regularly using public transportation, we go to the library, farmers market, grocery store, various parks. Other activities we save for days when DH is not working. Usually we can only travel all together, but recently I took a couple trips with the kids and without DH (he had to work). On one my dad went with us, and my best friend was there for another. I was surprised how well those trips went (including flying cross country with a toddler), I had thought it would be harder than it was.
If you choose to continue your pregnancy and parent this child, I think you will find your reality much rosier than you expect it to be. Whatever your choice, I hope it brings you happiness.