One of the major themes in the story of Samson is his getting in trouble with forbidden women in order to - apparently unwittingly - cause great harm to the Philistines. Whether love of lust, all of these relationships were outside of the Law of Moses, even the first one - which at least involved a marriage. Because of this, it is appropriate to think of them as lust, but a lust that was somehow used by God for a providential purpose.
Judges 14
1 Samson went down to Timnah where he saw one of the Philistine
women. 2 On his return he told his father and mother, “I saw in Timnah
a woman, a Philistine. Get her for me as a wife.” 3 His father and
mother said to him, “Is there no woman among your kinsfolk or among
all your people, that you must go and take a woman from the
uncircumcised Philistines?” But Samson answered his father, “Get her
for me, for she is the one I want.” 4 Now his father and mother did
not know that this had been brought about by the Lord, who was seeking
an opportunity against the Philistines; for at that time they ruled
over Israel.
In the end, Samson's ungodly marriage leads to a great slaughter of Philistines, which the author implies is a great good. As similar principle is involved in Samson's relationship with the prostitute of Gaza. This time there is no slaughter of the Philistines, but they are put to laughable shame by Samson's foiling of their plan to ambush him.
The story of Delilah completes to sequence. He falls for her, the Philistines entrap him, and he turns the tables on them yet again. So Samson is consistently misled by his sexual desires, yet the unseen hand of God is somehow with Samson. Every time Samson gets into trouble because of his lust, God turns his fall into a victory by enabling the hero to either put the Philistines to shame or slaughter them. Looking beneath the surface, it is not a story that is easy to square with modern understandings of the way in God works. One can only imagine what a truly great leader Samson might have been if he had used his sexual energies to build a model family and lead the Israelites to unite as a nation.