Family or BF 1st?

So my BF and I been arguing lately because he says I seem to push him back when I really don't. So my sister had her baby recently and asked me if I can take her to the doctors in the morning. I usually take my BF to work at 10 and her apt is at 9:15. Well to cut it short he gets mad when I chose my family over him cause he says he should my 1st priority. In my case I don't think so my family will always be 1st and I wrong for this? Th one time I ask him if a family member can take him to work cause I need to go with her due to her not being able to drive she had a c- section. Would you do the same chose your family over your man?