Now I'm not marriage counselor...heck I can't even get a boyfriend but given my interactions with friends and loved ones I think when things become routine and you find yourself dwelling on those negatives stop and think. Think back to what attracted you to the other. Find a way get back to that beginning stage of exploration. Some people are going to say "But I know all there is to know about my spouse (or friend)." I hate to break it to you but people change. If your memory is a lot better than mine ask old questions and see if the answer changes. Try new things together, try old things together. Try to bring that fire back.
If after all of that you realise that it's just not going to work out at least you know you gave it your all. If it does work out then you've gotten a new leaf on life.
My two cents.
-The Empress