I simply do not believe that a loving God - a belief I was taught - would have your boyfriend murdered to punish the two of you for having an abortion. I simply do not believe that.
I also don't think the grieving process is any different if it's death by homicide than if it's death by natural causes or any other event - loss is loss, grief is grief. Perhaps if it's other than natural causes you can find someone to blame and that makes it "easier" (if that's the right word) but I doubt it.
My husband died from natural causes and there were days I simply didn't know how I was going to go on. It's a hollow thing to tell you and I know it but you have to go on for the sake of your child. You have to simply believe that it will get better for you.
You've been dealt a hard, cruel hand and nothing I can say will make you feel better - but you have to go on for your daughter.
Remember that he loved you and that he didn't want to leave you. I hope that gives you some comfort.