Bastiano killed himself so the narrative would no longer have to deal with him cockblocking the endgame couple, the only one that really cares is one of the maids, and Garda is, as she was before Bastiano showed up to play antagonist, hopelessly in love with Starke.
This sure is an ending. Don't particularly love or hate it. It is just there. That sure was a novel I just read.
There were points where the romance was interesting, but it just ended up falling flat due to conflict management.
Like, in the flashback to reveal the backstory to how Bimby was born, O'Neill showed us Starke thinking about how people just kept heaping adversity on Bimba and she was expected to just take it and how that's sad. And then he went to add onto her list off adversities by knocking her up and running away for months, leaving her to deal with a pregnancy that eventually left her disabled. We do get something approaching an admission of feeling guilty when he expresses his feelings that he's tainting Garda, but because Garda is just such a pure soul(and also had not found out his secret yet) , she doesn't seem to totally buy it
Then, Garda finding out about him hurting Bimby doesn't really alter their relationship that much. I,as the reader, get to find out that he didn't mean to hurt Bimby, and that he did seem to have some genuine feeling for Bimba, but Garda never does. She hears from Bastiano that he had a secret lover and he threw the baby on the floor, and she never talks to Starke about it. She just assumes there's this good explanation that she's never heard before to justify it.
Starke mainly seems to feel guilty about the Bimba situation when he's made to think about it from someone else alluding to it, and at no point does it feel like he's guilty because his actions betrayed his love for her. It feels like the tragedy is supposed to be "oh, he was just a young boy making young boy mistakes and now he's haunted by the consequences of them as a man" but that angle doesn't work because 1. I don't view making a baby as a little whoopsie , so I hold it against him full force and 2. Bimba bore the worst consequences of what they did before she died. He was man enough to try the "leaving for milk routine", and he's man enough that I think he's a dickhead for trying it. I'm not pitying him for having to raise a disabled baby he fathered to begin with because he got handsy with one of the maids. Boohooo. Should've kept your pants up or stayed your ass in Italy dodging responsibility like it's the draft, playboy; at least then, you wouldn't have had the chance to drop Bimby.
Also, it feels like the story leans into "the last/endgame love interest is the only one the character truly loves.", which is one of those things that can make my feelings for the main couple take a major hit depending on the writing around it, and it definitely does here. Starke doesn't mourn Bimba after she's gone; he just gets tense when she comes up like he cares that he hurt her, but not because he necessarily loved her in the way expected of lovers. He cares because he knows that if he'd left her alone, she'd probably have been better off. Once Bastiano offs himself, Garda doesn't seem that mournful despite saying she'd have liked to have both him and Starke as lovers at the same time twice. Her grief is focused entirelly on Starke. Arguably, this could because Bastiano is confirmed dead while Starke was only on the brink of death(and eventually survived). However, the fact that just hearing something bad about Starke made her lethargic and passively suicidal while hearing that Bastiano died doesn't affect her anywhere near as badly doesn't reassure me that she actually loved him.
When Bastiano is gone from Garda's side pre-death, she doesn't seem to care about him at all, and when he is around, she is still pining for Starke. It doesn't come across like her heart is being pulled in multiple directions by genuine love. It makes her seem fickle.
Narcissus notes that it would have been better for Garda to have just ended up with Starke to begin with, and because Garda and Narcissus are talked about multiple time as being parts of one whole, this could be seen as an admission that she should've just committed to one man, and that man is of course Starke.
Once Bastiano comes into the story, he's the main threat and he's not a particularly strong one. That could've been balanced out by Garda and Starke having more doubt in each other or their emotions causing them to push apart from each other more before ultimately coming back together,but Bastiano takes up a lot of the space where that sort of conflict could go. If Garda actually loved him enough for that love to be a threat to her relationship with Starke at the time we got to see him, I'd be fine with that, but it seems like they had a whirlwind romance and then the honeymoon phase stopped long before we got to see it, and it kills his threat level.