Thats very obvious, Holly wasnt planned as a Loveinterest Character.Unfortunately, no.
Without cheating on Lexi, there is no Holly.
I don't know why Drifty wrote it this way, it doesn't really fit the rest of the game.
Drifty didnt expect her to be this popular (dont know why, she is incedible hot and sweet). After her appearence there were so much people out there who wants a realtionship with her and the MC, drifty was surprised by that. Nearly every Patreon poll, Post, or any mention about Holly get out of Hand and he realised that Holly needs to get more focus in the Game too... But it was already "too late" to establish something with her and the MC the "right way" like with all the others... so he needs antoher solution, cause it was always the plan to make a optional threesome with Lexi he decided to set some triggers there that will ultimately lead to some more with Holly at a time.
Another way would be to rewrite the first chapters with Holly in it to establish her in antoher way, but that was never the plan about her... I think he tried to pull off a Holly relationship as a "fanservice" here. I like it that he decided to do so, but i admit i dont like the way it is in the game, but i dont think there is any other way to do so at this point... cause as i said, to do it in another way, drifty needs to rewrite some things in earlier chapters.
Although i think its a variety in the game to have to cheat to get another girl... most of the realtionships are very smoothly running. But if youre on the Robin and Kira path, and decide to only be with one of the girls, you can see that it fits in the game that not everything runs out smoothly in the romance sector. So overall the Holly thing does fit in the game, it doesnt feel right to have to cheat on Lexi, but it fits...