Well first of all he should be paying for at least half of the procedure. You have to keep in mind this is a stressful situation for you both. Babies are hugly life changing. Having a kid you don't want or plan for can de-rail plans, cause huge amounts of emotional/mental strain and potentially ruin your life. You are making a wise decision. Your boyfriend should be supportive of you during your abortion. I think he is nervous you are going to change your mind. People handle stress differently. Making it seem like you're going to keep it is stressing him out even more.
Make sure you treat yourself after the procedure. Buy some candy and take a self care day. Your boyfriend will most likly come around to support you after the procedure.