I'm so sorry to hear you are feeling this way.
While it's important that people can share their feelings - in any way - post termination, please do also be aware that these threads also attract people who are (a) anti-abortion and know they can post here to tip the balance for future women who do an internet search for 'regret abortion' and (b) people who like one poster here sound like they are living very complex lives with severe mental health issues and 'several abortions' when just into their 20s. There is nowhere I can think of here that would perform a termination without clear consent/signature on forms as claimed earlier.
Many of us feel some regret with time, but also an acknowledgement that ultimately it was the right thing to do at the time - like how you might always harbor some feelings towards 'the one that got away', while knowing that it wasn't right for you, in this lifetime. Trust your past self, it's easy to second guess now you know it's over.
Do also be careful that you don't feel so full of regret and hormones that you get pregnant again asap, I have 2 friends that have done that, and it makes everything ten times harder, when they realised once pregnant again, that pregnancy really wasn't right.
All the best. Please do speak to a counsellor if you can, you shouldn't be going through this alone and in my experience this isn't one that's easy to talk.about with friends and family as they all bring so many of their own feelings and beliefs to the discussion.