The only way to force him to pay is by taking him back to court and seeking a court order compelling him to pay the previously ordered or agreed-upon alimony. In the process, if his payment is in any way based or conditioned on the amount he earns (e.g. you get a percentage or share of his income generally or bonus specifically), you can also seek  "discovery" (information and documentation) about his income, to ascertain how much he makes and therefore owes you. Speak to a family law attorney, as you threatened, about doing this; again, a legal action is the *only* way to force him to pay and/or reveal information.