The heaps and bounds you're willing to go through just so you can avoid having Richard and Isabella married despite all non-Angevins candidates post-Baldwin V being related by marriage to them is a little ridiculous, once again they were related far apart among medieval nobility to not have any issues despite very possibly requiring a Papal dispensation.
The POD is the invitation of the Patriarch for a Prince of the Realm (either English or French) to accompany him back to Jerusalem in 1185. This is when the Kings England and France and the HR Emperor all pledged to go on crusade (and in the case of Henry II and Philip II, not being anxious to actually go themselves).
Sybilla and Isabella were first cousins of Richard's father, and both were married by that point. Yes, Papal dispensation for wedding first cousins did happen, and annulments for consanguinity between second cousins did also happen, but we are talking about a Papal annulment followed by a marriage of first cousins involving a groom who historically was reluctant to marry....
Guy was deemed unsuitable by both Baldwin IV and several of the principle commanders, especially the Count of Tripoli. The fact that Guy had seduced Sybilla prior to marriage very likely did not help in this regard.