I'm an advocate for letting go. It goes with my whole "care-free-hippie" shtick. Walking away from things is the easiest thing for me to do. But as I grow up I realize that sometimes you don't need to; and quite frankly, you shouldn't always. You can't go around letting go of every relationship or situationship that challenges you. Challenges are necessary for growth. What's difficult is deciding which ones are worth the challenge.
Sometimes staying and fighting is completely warranted and completely worth it. I believe strongly in this statement that I heard on a Dr. Phil show a few years ago (no judging. It was a random show I'd watched, and I don't subscribe to his show regularly). Anyway, he said that you have to fight your way out of every relationship.
As asinine as it sounds, the reason this statement is so important is because it tells us to tap back into that innate sense of resilience we were born with. It also reminds us to be patient as It encourages self-reflection. Most importantly, it teaches us to respect and value the relationships and the individuals we share them with.
I'm naturally a runner; physically, figuratively, and emotionally. I love being able to live freely. I hold no grudges when I leave relationships or when they leave me. I chalk it up to, "it just wasn't meant to be". While this works 100% of the time, what I've often failed to do is to give relationships the respect they deserve, and to give clear reasons to an end outside of "this just isn't working, or this just isn't for me, etc".
Take time, and give yourself some credit too. You are in your situationship or relationship because you chose to be there. You hold 50% of the responsibility. You chose to accept the job, you chose to be friends, you chose them as a lover, etc. Obviously don't stay and fight if your situation is abusive and endangering to yourself in anyway. But when you do want to leave, consider staying too. Weigh the pros and cons and make an informed decision. Don't run so fast. Fight until the bitter end if it's worth it. You'll be happy you tried everything you could have.