Well, there was one time in Busiek's run... She kissed him in gratitude. Clint quickly pushed her back all gentlemanly and all, and they hugged it out all platonically. Really sweet scene.
That's not really what happened and it wasn't sweet so much as pathetic.
Melissa had the habit of jumping into relationships because she wasn't independent which always caused her problems (Agnar, Abe, Mike the boyfriend she went to jail for). She threw herself at Clint because she wanted a man to protect her and fix her problems...even though her boyfriend Abe just turned himself over to the police a few issues before to help secure her a pardon. Karla later called her on it after she herself seduced Clint.
That's pretty much the same thing I said. Clint's reaction was the sweet part.