Thanks for the background information, it makes understanding your situation and who you and your boyfriend are much easier.
As for your question, No I do not think you should allow anyone to make you feel that you should have a abortion simply because you made that choice in the past. Even if it means moving home and being a single parent. The fact is this is your body, your child and your choice. What happened in the past is simply the past.
When you made the choice to abort the first time it was for a valid reason. You were on medication that could have caused serious problems for the child........and you made a choice that was in the best interest of the child as well as your gut instinct that told you that this was not a good time.
This time around there are not the same issues at play, there is no threat to the unborn child. While I am sure now is not the perfect time..........when is it really? Children are a miracle and as such when you become pregnant you must look at all the angles and what is best for you. This is not a decision you should make based on how your boyfriend feels or his family feels, because the fact of the matter is if you go against your own desires you will resent him for what you will feel was a forced abortion. Since you feel so strongly against abortion in the first place, it will be even more difficult for you to heal from this unless it is something you really want to do.
You already know the downside of abortion, I will not color the truth by telling you it gets easier or you will get over it. Being a man I have never had this issue of course, but I have done enough research on the issue to know the sad reality of the depression and guilt that follows a abortion a women did not really want.
In the end this is your choice, and no one including me can tell you what is best for you and your child. As for his family, yes they may have some issues in the beginning but you can not allow their choices to effect yours. If you choose to keep this child then they are the ones making the choice to either accept the child or not.
I would suggest that you sit down with your boyfriend and explain your reasons once you make your choice. Let him know that while yes you did make that choice the first time the reality is you did it more for the health of the child then the desires of the boyfriend and while what he wanted did factor into it the reality is it was something you had problems forgiving him and yourself for.
Let him know you are willing to get married if that is what he wants, and are willing to speak with his parents about your reasons. Then be firm about your choice.....he may become upset, or he may take it and get over it. The fact is he will likely be at least a little upset about it as this is not where he wants to be right now. But if he really loves you and is a good man then it is something he will come to accept.