In the Day Watch novel by Sergei Lukyanenko and Vladimir Vasilyev, at the end of Vitaly Rogoza part, we discover that
Zabulon sacrifices Alisa because he wanted to remove Igor Teplov.
Was his previously stated love real? Was he just using Alisa for the whole time?
I really doubt it - at best he might have loved her in a way you love your favourite tool. Great Dark and Light Ones have plans within plans and are not afraid to sacrifice their peers for own gain. Alisa is one such case:
The whole action of the Night Watch novel revolves around Svetlana's rise to power as a Great Light Enchantress and about Day Watch trying to prevent it. When the gambit with vampiress hunting for Egor and Svetlana's self-cast curse doesn't work, Zabulon starts his "Plan B":
He knows that Anton will be opposing Gesar's plan to use Svetlana as a "general in the war against Darkness" (because this would make the Anton-Svetlana relationship impossible), so he picks Alisa, and as the proof of his love, he gives her a powerful artifact allowing to steal life (and power) from unwilling victims. Now, after giving Anton a big speech about the dangers of the Chalk of Destiny, Zabulon puts Alisa in Anton's way, knowing that she won't be able to resist using the artifact and, in effect, getting arrested. And here is the little masterpiece:
'I confirm the pledge made by Alisa.'
He seemed to be utterly serious. I swallowed. A promise like that from the head of the Day Watch . . .
'Never trust the Dark Ones.'
'Any intervention up to and including the second degree.'
'Are you that eager to avoid a scandal?' I asked. 'Or do you need her for something?'
A tremor ran across Zabulon's face.
'I need her. I love her.'
'I don't believe you.'
'As the head of the Moscow Day Watch I ask you, watchman Anton, to settle this matter amicably. It is possible, since my ward Alisa Donnikova had not yet caused any significant harm to humans. As compensation for her attempt' – Zabulon emphasised the last word – 'to perform a magical intervention of the third degree, the Day Watch will accept any Light intervention that you may perform up to and including the second degree. I do not ask for this agreement to remain secret. I do not impose any restrictions on your actions. I confirm that for the offence she has committed Day Watch agent Alisa will be severely punished. [...]And the right to carry out a second-degree intervention that Zabulon had granted me so generously was a trap. There wasn't any doubt about that. He'd framed his own girlfriend, drawn the lines of probability together so that we'd meet and then handed me his deadly gift with a mournful expression on his face. I couldn't see far enough into the future to be sure the Good I did would never become Evil.
And when Anton starts to use his gathered power:
'Don't do that!' Gesar shouted. 'Don't you dare!'
In one swift movement he dashed across to shield Svetlana and Egor from me. As if that could stop the spell. There was nothing that could stop it now. [..]
Zabulon laughed quietly behind my back. [...]
smiled at Svetlana. And very slowly raised my palms with their fountain of rainbow light towards my own face.
'No!'
Zabulon's howl didn't cut through the roar of the hurricane, it completely drowned it. A bolt of lightning flashed across the sky. The leader of the Dark Ones rushed towards me, but Gesar stepped out to meet him, and the Dark Magician stopped.
Immediately after this gambit, Alisa is discarded as a love interest: Zabulon who was lovingly touching Alisa's hair in front of Anton just to drag her brutally moments later) - that is until Zabulon needs her again, this time to remove Igor, who would guarantee that Nadya, a future Absolute Level Sorceress, would join the cause of Light. So Zabulon again uses Alisa: he gets her exhausted in a meaningless battle, feigns the love again, sends her to recover and meet Igor, who believing that Alisa was using him kills her in a duel and later commits suicide out of guilt.
Zabulon was "in love" with Alisa when it was necessary for his plans, discarding her when she wasn't needed.
The text doesn't say anything on what Zavulon's own internal thoughts or feelings on the topic were (I re-read entire " Day Watch" to double check). And made plenty of points that at the level of Geser and Zavulon, any external indications are not to be relied on.
The closest to a textual answer can be the dialogue of Edgar and Inquisutor Higher Vampire Vitzeslav at the last page of "Day Watch":
Инквизитору надо иметь хороший слух. – На лице вампира появилась кривая ухмылка. – Да почти ничего. Я бы назвал это проклятием, но Светлые и проклинать-то не умеют… Она сказала: «Пусть никто никогда не полюбит тебя».
Эдгар кивнул. Пожал плечами и сказал:
"А ему это и не нужно."Edgar carefully took the crumpled gray material out of the vampire’s hands. He asked awkwardly, “I beg your pardon…but what was it that Svetlana said to Zabulon?”
“An Inquisitor has to have good hearing.” A crooked grin appeared on the vampire’s face. “Almost nothing at all. I’d call it a curse, but the Light Ones don’t even know how to curse properly…She said: ‘May no one ever love you.’”
Edgar nodded. He shrugged and said, “He doesn’t need anyone to, anyway.”
One can surmise that since Zavulon doesn't need anyone's love, he most likely doesn't love anyone, as - if anything can be assumed about a subject as subjective and vague as "love" - we can assume that when you love someone you need them to love you back. But that is Edgar's opinion of Zavulon, not necessarily truth.
