There are a lot of good suggestions here.

Reading religion and philosophy definitely helps. A good way to get into that is to find a writer you like (can be anyone) then find out who their influences were. I've enjoyed reading Joseph Campbell and Alan Watts.

Exercise is a great thing as well. It's surprising to me how extremely positive a force daily exercise is in my life.

Writing, therapy... all really good things to consider. You have to find what's right for you. That's a hard thing to do when you're in a slump.

You need a challenge or, even better, a challenging journey. Have you traveled seriously or lived in another country? If not, do it. Go with your fiance, spend at least a year in a foreign place.

Good luck.