Lots of good suggestions above. One thing to consider is that maybe you don't have the personality for long solo hikes.
I started running back in high school and immediately loved being out on the roads and trails alone for hours at a time. This was long before portable music players, fancy watches, HR monitors, or GPS units.
Later I got into cycling and found the same thing - I loved being out there for hours and never got bored. People would ask if I got bored and the question did not compute.
However, I've got a lot of friends who would find these activities boring as hell. They love to exercise, but it has to be a game - Ultimate, volleyball, soccer - anything with a score and other people to keep them interested. I notice that these friends would rather watch a movie than read as well. Nothing wrong with it, it's just their personality.
Long way of saying, maybe you'd be better served sticking with activities that suit you.