I have buttermilk stored in my freezer since late jan the expiration was jan 23rd, is it still good for me to use?
Yes, it's fine. Freezing does not allow spoilage.
By the way, I bought 12 silicone cups (1/4 c each), put them on a cookie sheet, and filled them to the top with the quart of buttermilk. After they froze, I popped them out of the cups and put them in a zippered freezer bag. Now I can take out exactly what I need.