You can do it!
I'm on a similar boat as you. I'm 17, pregnant, and the father isn't part of the pregnancy and won't be part of the babies life (he was trying to control the situation and manipulate me, when he couldn't have things 100 percent his way he refused any responsibility. His attitude now about his child is "i'm not doing anything until the law makes me").
Boys that can do what your boyfriend is doing in hard times like this, will still be the same person and do the same thing in the next hard time. Their thinking only about themselves, and how to get what they want. He should be thinking about you, and what type of toll abortion will take on you and what it is you really want to do. Your boyfriend is 28, and an adult. He should be able to step up and deal with whatever you choose to do, and if he can't do that, then he is just a little boy.
It's so wrong that he's given you an ultimatum. By telling you he'll only provide his support and care if you do what he wants he's proving his love is conditional, and love doesn't work like that. Just remember, the love you and this baby share will be unconditional, it will be amazing. Is that worth to sacrifice for a man who's love is already wavering, who can't stand up and be there for you when you most need it?
Many girls who have had abortions deal with it for years. Think if this is something you could live happily with in the back of your mind. Abortion and keeping the baby aren't the only options, there is adoption. I'm sure adoption will atleast give you the piece of mind that you did the right thing if you decide you are unable to keep the baby where abortion might leave you hurting and full of guilt. This is your choice though, and whatever you end up deciding do it because it's the decision you've made with your heart, not because someone else manipulated you into it. Good luck!