There is something about the word "selfish" that doesn't sit well with most people. Being selfish is an indication that you would take from someone else for the mere reason of wanting it for yourself. There seems to never be a context where it is used when the consensus deems it OK to be selfish.
Webster's Dictionary defines Selfish as "concerned excessively or exclusively with oneself : seeking or concentrating on one's own advantage, pleasure, or well-being without regard for others".
When you focus on the success of your career it is not a selfish act. It appears that way because you don't spend time sitting idle listening to chit chat, there may be events and social things you "always" attended that you can't seem to fit into your schedule now, and when it comes to your waking moments you "without regard for others"; this is not a part of the thought process.
In focusing on your career, you still show much regard for others. Regard for others means you think enough of them to call and explain why you can't _____. Regard for others happens when you don't say you're going to do something which you know before you say it you won't be able to do. You don't set anyone up to be disappointed by any negligence on your part. It is the thoughtfulness you have for others which causes you to keep them on your calendar.
No, you can't chit-chat like you were before, but a text message and daily email is doable. No, showing up to the weekly happy hour isn't on your agenda but you wish everyone going well and to have a drink in your stead.
Changing your actions to be career focused doesn't mean you're selfish. On the contrary, it just means you are Self Focused and moving toward the successful career you know you are capable of. Will this be your forever life? Probably not, but a habit has to start someplace and starting now changing your routine into one that is pointed toward success is definitely a good habit to start Right Now.