I really couldn't tell you why, but I just couldn't do that again.
This was a difficult decision for you and you worked out the rational reasons why an abortion was the best decision for you. It sounds as though your instincts were struggling with the decision with lots of tears, going back and forth over the options, and feeling that you could never do this again. Thoughts and instincts are often very polarized, and I think we sometimes suppress our instincts or feelings to do what seems logically to be the best option. Perhaps your feelings are surfacing a bit more and making you feel uncomfortable with the thought of abortion. You certainly went through quite an intense time of pain and sickness, which must have been frightening at times.
I hope you will call the national helpline if you feel you need to speak to someone about how you are feeling.