I am every so sorry you are in this dilemma, FightingWiththeWind.
Nobody likes abortion but people have them because, at the time, it is the common sense decision. Put your sensible hat on.
Though I believe nobody has the right to 'force' any woman into an abortion, neither could anybody blame your partner for feeling the way he does. Another child in a two bed place, if there is no prospect of being able to buy somewhere bigger in the near future, would make life very difficult.
It sounds as though your life is pretty settled as it is.
In your position, I would not have another child.
You will get over it, honestly. Act quickly. You will receive plenty of support on here. In a year's time you'll be glad, not in a 'celebratory' way but you will be counting your blessings. At the moment, hormones are playing a part in your feelings but they will get back to normal.
What you need to do then is make sure you do not become pregnant again, belt and braces' if neither of you wants to be sterilised.
You said: "I'm angry that my friend has 4 children, doesn't work and has a 3 bedroom house and never had to consider not being able to afford them; I'm angry at myself for feeling that way..."
The fact that you're angry at yourself for feeling that way shows that it is an unworthy feeling. Don't resent your friend for having one more bedroom, not many people want four children! Comparison is pointless and resentment eats away at you. You have a lot as you are and in time, will no doubt have more.
Good luck and chin up.