Piano/guitar improvisation trouble?

I started piano when i was around 5, and didn't take it serious until around 8 or 9 or so, I'm 17 now, and I haven't played for a year or so. The reason for this is that I find myself simply not knowing what to play, i consider myself to be a fairly accomplished piano player, but I have such difficulty "letting go" so to speak. I started guitar when I was 10 and I have the same issues as I did with piano. I'm starting to slow down how much i play guitar because I'm running out of things to play, I can only play so many of my favorite songs so many times until it's boring. I'm better at improvising on my guitar, but there's only so much I can do until I just think "well.. what else?". I'm afraid I'm going to lose the desire to play both instruments, and I feel like they're both extremely important things to know how to do for the future. Music is a huge part of my life, and I just need a little direction to refuel my passion. Thanks in advance for any replies.