If you have an injury arising out of the course and scope of employment and you properly reported it, resignation will not prevent a claim (assuming your statute of limitations has not run). If you sign a severance/general release from employment this would not be a bar to a Florida claim assuming you were not represented by counsel when you signed it. In Florida, an unrepresented claimant cannot settle or waive rights unless a workers' comp judge approves the agreement.
You're not too late. With a repetitive trauma case like this, each time you work you are exposed to the trauma of lifting, pushing and grasping. You could report to your boss that you want to make a claim and believe you have injured yourself. Your "date of accident" would be the date last worked even though you have been having problems for some time.
Based upon your post it sounds like you have requested a hearing with an ALJ and if your case was with a decision writer, that is good news for you. (They don't get a decision writer involved to write an unfavorable decision if you haven't had an ALJ hearing.) Based upon what you've said it looks like you may receive an On-the-Record decision, and since the file is back at ODAR you probably should be hearing something soon. "Soon" is a relative term.
You indicate that you've been approved for ssi/disability but state your ssi check "isn't due" until the end of March. In order to answer the question, it's important to know whether this is an SSI only case, SSDI case, or concurrent case (both SSI and SSDI). SSI entitlement is done on a monthly basis and it appears that you are concerned that the UE benefit count as income and cause reduction or elimination of your SSI benefit. Unemployment is indeed income and will count as income in the...
If your boyfriend's "disability income" is Social Security Disability (on his own ss number - not as a disabled widower), whether he marries you will not impact the amount of his Social Security benefit. However, based upon your joint income some or all of his Social Security may become taxable. Go to www.ssa.gov to research the details on taxability. I'm assuming he's not getting SSI because he's receiving $1800 per month.