At times, when I am reading a book, watching a movie or when I am brave and venture out for a walk, and I see a couple, then that is when my mind begins to wander into that "gosh, I feel alone and lonely" but fades once I keep my mind busy - I find, for me, anyhow, it has helped me to keep my mind (and body) in motion, for lack of better words. Just simple housework, choosing a netflix movie or tv show that you know is gonna make you laugh your butt off and at least for that moment, just be.
Eckhart Tolle, someone mentioned, is a definitely good book to read. Sometimes it is hard to find 'that balance'
If you dwell on things long enough, it seems your whole world is consumed by those thoughts and feelings. Hard part is, though, stopping or momentarily halting those thoughts and feelings and trying to be content....easier said than done.