It is paramount that you go with your gut when making decisions. No matter what you call it (conscience, intuition, the Holy Spirit, -Ing) there is an internal compass continuously guiding you towards the unique opportunities and right relationships that are meant for you. Listen to yourself.
There are always signs or red flags alerting you to emotional danger. Pay attention to them. If something doesn't sit right with you, take some time to feel it out before making a decision so you can be sure to make the right one.
This is not, however, to be confused with succumbing to fear. Often, when fear is present, there's an accompanying nervousness--a feeling of not-knowing--that seeps in. But I have found that there is a sense of calm and near certainty that abounds when we sense innately that something isn't right for us. There is a distinct difference between these two feelings.
Sometimes there is a feeling that we might be missing out on something if we say "no" or we walk away; but rest assured that what is for you won't miss you. It, he or she will be there waiting when you are ready--if these things are meant for you, it is impossible for them not to show up for you. By letting go of the things that are not for you, you're making room for possibility.