How do I file legal separation when heis one state and I am in another?

If you meet the residency requirements for filing divorce in Florida, then you can file in Florida.  In Florida, the law requires that you reside in Florida for at least six months before filing.  Otherwise, you would have to file in the jurisdiction where you were married, which appears to be Pennsylvania. When you refer to filing legal separation, it sounds like you are referring to the date of separation during the marriage.  The date of separation was likely triggered when you left the marital residence. You should consult with a divorce attorney in Florida to determine your rights.  It is important to note that the state where you file is important, because different states have different laws regulating child support, custody, and so forth.