after all the trauma cath went thru grissom realises that it's her he really loves. he always thought that he didnt stand a chance with her so stayed back. now he knows that he will hurt sars bt revealing his true feelings for cath so has to go away to sort things out. when he comes back he tells cath how he feels and they get together. he finishes with sara and that causes her to start drinking again and she goes off the rails but tries to hide it from the others.it's only greg who sees that there is something wrong and covers for her hoping that they will get together. she tells greg the only reason she got it together with grissom was so she could get closer to cath thru him, she really wants to be with cath.