OMGosh! An abortion is NOT the Answer!
I'm sorry, but people say and do things that we cannot control. I'm also sorry that those girls are being so nasty to you. You don't need that stress especially while pregnant. I would recommend looking for a job change. Wither you admit that your friend is the father or say it's another guy, they obviously have it out for you and are not going to stop regardless of your answer of who the father is.
I would also recommend telling your friend that he is the father. If you are as good of friends as you say, and you were "his shoulder to cry on" then he should be there for you. He also should know that he is the Father. Whither he takes accountability or not, you need to let him make that choice.
Only YOU can decide how to raise your child. If you want to love it and care for it then do it. There will Always be someone or something bringing you down, at times even yourself or your child will bring you down. You Just Need To Stay Strong.
I wouldn't lie. Lying just increase stress and then what would you tell your baby when they inquire who their father is someday?
Try to switch jobs
Tell the guy ... and then take the next step based on his reaction.
Remember, "NO ONE CAN MAKE YOU FEEL INFERIOR WITHOUT YOUR CONSENT"
Best of Luck to YOU & YOUR BUNDLE of JOY