People feel nostalgia, loss and greif over a change from an old way of life. It is only natural. If you were comfortable or enjoyed that way of life for a while then those feelings come.
I think you are quite right, each move you have made now, job, flatmates and all, they are taking you further away from your old life.
While your logical mind may say I'll never go back (and be right) the heart can still yearn at times .
I'm afraid there is no timetable. New events will take over but it's hard at the start.
I was invalided out of my occupation which had nearly killed me, however afterwards I missed it like nothing on earth. There too the logical bit of me understood my situation and that my loses were permanent, the emotional side was not as well behaved:(
I've no profound advice, simply to look after yourself (nutrition, exercise, sleep) and find things to occupy you and for you to enjoy. - and that includes people
Please let us know how you get on