Crabs - It could represent a "crabby" or unpleasant personality or emotion. The claws could be symbolic of a clinging and hurtful person, or a side of your own personality. There may be too much dependence, clinging and forcefulness in your life. The crab may also symbolize your inability to effectively move forward and address your own difficulties. (Remember the crab often moves sideways or backwards.)
On a more positive interpretation, the crab could represent your perseverance and tenacity.  As with all water dwelling animals, the crab could also represent something in the subconscious and the emotions.

Mud - indicates problems in which some internal cleansing is needed. Walking in mud, suggests that you are feeling weighed down by a situation, problem, or relationship.

Going for the door as it is closing - suggests a need to escape, or reaching for an opportunity, but missing out or fear of failure.
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Are you wanting to end your current relationship, but are afraid to?
Is there something about Shane that you would like to see in your current boyfriend?
Have you and your boyfriend had an argument recently, and it has made you crabby, or angry?

I hope this gives you some insight, good luck!