The Spanish Tragedy was written between 1582 and 1592 and performed first in 1587. If we talk about the development of Elizabethan tragedy, this play describes us about the battle and later after so many deaths, the revenge will take place. I personally believe that the plays which were written by the University Wits and of course Shakespeare are so similar. Only the outline changes but other than that all remains cliche.
Although there is one character to focus on in this play, it's Bel Imperia, how she is the lover of Don and later she is in love with Horatio and such a staunch lover that she takes revenge for him. The irony is, she did not give a damn about Balthazar until It came to the death of Horatio. She did nothing when Don Andrea died. Sad. No lament?
Can we say that maybe she liked Horatio when she was in love with Don and she got to know him as he was a good friend of Don. And out of all the men and women(we don't know about her preference), she fell in love with her ex's dear friend. Seriously Bel?