Hi OP, so sorry your going through this 
My own experience happened when I was just 18 and in my first proper relationship and it was actually a good relationship. He was older and settled in life career/apartment etc. We were living together but still obviously early on in our relationship. The week before my birthday I found out I was pregnant, I was so so shocked as was my DP at the time. Literally within about 48 hours of finding out I was suddenly unbelievably unwell, I couldn’t eat, or drink or anything, everything made me sick. After 3 days of doing nothing but dry heaving and throwing up bile I was delirious so my DP decided to take me to hospital. I was treated very poorly at hospital I was told nothing could be done, it was just severe pregnancy sickness and to just go home and get on with it. At home I struggled on sucking bits of apple and sipping water, I could barely lift my head off the pillow for my birthday and I had lost a stone in weight and I was only 7 stone to start with. A couple of days later DP bundled me up in the car and said we were going to the doctors, I was so out of it I really didn’t care if we were going to the moon. At the doctors office I didn’t even make it to the reception before I was in the loo being sick. The staff saw how ill I was and whisked me straight into a room, I vaguely remember being asked to confirm my name and date of birth and being given a scan. Everyone talked like I wasn’t even there, I was so out of it I didn’t have the strength to speak let alone ask questions. I do remember them being sympathetic towards me and some nice lady patted my arm and squeezed my hand. I was sent home, nothing was said yet the next morning I was taken back to the doctors office. I was the first appointment of the day, I had be carried to the table as I couldn’t even walk. Some nice lady helped me dress into a gown and held the sick bowl for me as I was being sick and at the same time a man performed a surgical abortion. I don’t know if I was even given any pain relief because the pain was the thing that brought me round from being delirious and I shouted no, but it was already done. I was 18 at the time, so 21 years ago and I had a procedure that I did not consent to. I had become so ill that it took a couple of months before I gained weight back and felt physically well. Those first few weeks I was in complete shock and still very sick and then slowly as my body healed my mental health started to suffer.
At first I was terrified of becoming pregnant as all I could remember was being so poorly, I had literally felt like I was dying. Then as the memories of the sickness faded I started to mourn my pregnancy and the child that could have been. Then I was angry, so very very angry, angry that I was living with this pain and this trauma and the after effects of a decision that I didn’t even make, that was made for me. My DP made his excuses, said that it was so terrible seeing me so unwell, that he was frightened and this is what he thought would fix it!! I became obsessed with pregnancy and babies (I had never been before) yet anyone getting pregnant around me was like a very real punch in the gut. I told DP that I couldn’t cope any more and that I felt like I needed to get pregnant in order to recover (silly I know but being so young it was how I felt) DP of course refused. I felt so utterly bereaved and alone, no one apart from us knew I was ever pregnant in the first place so there was no one to talk to. It’s the most consuming pain I have ever felt, but it did lessen in time. It also helped that I now know that I was suffering from HG a severe form of pregnancy sickness, and I didn’t fail in some way, in fact there were drugs that could have prescribed to me that may have helped. Leaving my DP also helped, he was the source of my resentment and a constant reminder of what happened. It took me 4 years to leave but I did eventually leave, and it turned out to be the best medicine in the end.
Whilst our circumstances around abortion are different, I can very much identify with the pain you are feeling. For me I just wanted to be pregnant again for a very long time, but of course what I really wanted was not to replace the baby, but instead to not have aborted the one I already had, alas neither of us has a time machine so of course it’s not possible.
What helped me: I avoided anyone else pregnant like the plague for a good while. I bought a little teddy bear and a candle in remembrance and whenever I needed I lit the candle and hugged and cried into that teddy. I also did some crazy things that I’m not sure if it made it better or worse but since this is an anonymous forum I will share these with you. I picked names, one for a girl and one for a boy, I picked out the crib I would have put them to sleep in, picked the pram I would have pushed them round in and numerous other things and for a time I would daydream of the things we would have done together and the books I would have read to them, the songs I would have sang etc. It was easy to visualise and made me feel that somewhere somehow that despite what happened my baby was loved, just as you love yours too, because the choice you made does not mean that you did not love this baby, and does not mean that you didn’t lose a baby, it’s does not mean that your aren’t bereaved because you are and you are allowed to feel sad and you are allowed to grieve your loss because it is still a loss.
Please allow yourself some time to grieve, know that whilst the pain may be quite acute right now it will lessen with time. Please don’t feel guilty, (I felt tremendous guilt for a long time) you made the best decision, with the information you had at the time and for what it’s worth given your ex I certainly would have done the same thing. Try not to worry about the future unnecessarily, I was convinced for a long time I would somehow be punished by the universe and never be able to get pregnant again, I was wrong!
Nothing stays the same for ever, and while marriage and babies might seem far away now, or out of reach, it won’t be or feel this way forever.
You will heal, and if your struggling please don’t be afraid to reach out for help. BPAS also offer post abortion counselling as do Marie Stopes I think.
I’m sorry this post was so long 