Ghetsis was using him.
It was no astonishing fact given Ghetsis' very nature, but it was somewhat disheartening to accept. They'd had this odd relationship for years now, and Lysandre had been amazed to discover that he didn't mind how things were at all. His lover was using him - and he had to give Ghetsis credit for his subtlety - and Lysandre honestly didn't care as long as Ghetsis didn't decide to abandon him.
That was the astonishing part.
That this man had charmed him so thoroughly that he was helpless to resist manipulations that he was consciously aware of. That he was impressed by the feat rather than disgusted. That all of this had only further ensnared Lysandre in the man's hopelessly intricate web of subverted truths and endearing lies, when he should hate Ghetsis for leading him on in the first place, for using his damned feelings like this.
He didn't even know what Ghetsis felt for him, if anything at all. His 'I love you's were so very authentic that Lysandre scarcely dared to remind himself that lying was this man's profession - and one he'd clearly mastered, at that - by his own admission. He visited frequently enough from his covert projects in Unova that Lysandre, if he so wanted, could easily convince himself that Ghetsis had missed him, even if more often than not these visits involved a trip to Lysandre's superior laboratories. He readily accepted Lysandre's affection, and returned enough in kind so as to allow Lysandre to believe he was special, that Ghetsis had never done these things with anyone else, despite Ghetsis' tendency to gravitate towards men with a certain level of power and influence.
Lysandre's heart and mind warred over whether this was disheartening or awe-inspiringly beautiful.
It didn't really matter, in the end.
On the surface, Ghetsis was a loving, if slightly distant by nature partner, and that was all Lysandre needed to placate himself with. Ghetsis' true feelings were as unknowable as they were inconsequential, in the end - as long as he was willing to play the part, Lysandre was happy to play along with him, come of it what may.