I'm not sure that you are obliged to tell him. You feel like the going-out days are gone, and drinking and being careless, it's OK to tell him that. But don't rain all over his parade, if he is excited. He probably will come down from that, and you will come up, and the two of you will meet in the middle. But in any case, remember that a husband who is actually interested in and pleased about his wife's pregnancy is worth his weight in rubies, especially in the middle of the night when the baby is crying and you are exhausted. I always felt like I was treading on eggshells and that my husband was on the verge of blaming me for wanting kids any time something irritated him. Not a good place to be when a baby is young and will have moments where he or she is less than an angel.
Anyway, tell him wistfully that you are kind of sad for the feeling like your careless and carefree days are limited, and work out some ways now (even though you are just pregnant) to cover a few nights here and there for child care, so you can still go out. You can still have your careless moments, you just have to plan for them. lol Also, please listen when your doctor tells you the symptoms of post-partum depression. A feeling like this in advance of the baby being born is just a tiny bit of a red flag that you will have a feeling like that, after the baby is born. There's help for all of it.
ps -- I know that you will fall in love with your baby. :) Don't worry.
Once you hold your baby in your arms a love you never knew will overcome you and you will not care about going out at all. I have a house full of kids college age to 3 & you just learn how to manage & have mommy time thats important so you don't feel like you have lost yourself. I do agree with other poster pay attention to the "post partum blues" after the baby some people have them worse than others. If you need someone to talk to feel free to talk with me. Good Luck