Per the above.
I would also like to extend the question: what would the circumstances need to be, in order for the Crusader states to survive for as long as possible?
If we are talking about the Kingdom of Jerusalem, Principality of Antioch, and the County of Tripoli, and the County of Edessa you will need a couple of things. First, a larger peasant population. Unfortunately, after the battle of Hattin, the crusader states were only strong if an actual European sponsored crusade was occurring. Before the battle of Hattin, the crusader states could field a sizable force, but after this army was crushed, the crusader states were really only capable of defensive warfare by themselves. If you could get more people from Europe to move to the middle east and settle there, the crusader states would have the manpower to once again field an effective army without the help of a European power. Secondly, the Islamic nations in the middle east MUST remain divided, meaning that it would be in the Crusader states best interest if the Fatimid Caliphate survived. If Saladin can unite the middle east like he did in real life, Crusader States don't have a chance. Also, there are inter state rivalries that leads to political problems as well. It would be best if they are all unified under one state.
Those first three changes are necessary. Other changes that could help is if the Knights Templar can hold onto Cyprus, the Crusader States enact military reforms (Knights on armored horses don't work well against light cavalry and horse archers), NO FOURTH CRUSADE, naval superiority in the Mediterranean, and the capture and Christianization of Aleppo and Damascus (don't know if this is possible).
Also, In reality only Tripoli, Antioch, and Jerusalem can survive. The County of Edessa, although closest to the Byzantine Empire, is landlocked which means it will most likely fall. Not only this, but if we keep the Fatimid state alive (necessary), then the creation of Mamluk Egypt is butterflied away. This is important because the Mamluks are responsible for keeping the Mongols at bay.
If you do all this, the Crusader States will survive until the Ottomans come to power unless the Mongols wipe out the Crusader States first.