theory ahead:
I like the tomboy the most, to be honest, but this story is probably headed towards a choice between Manaka and Chisaki.
If it‘s a story about growth (which i don’t think this is), MC will choose Manaka and we‘ll see a happy ending, with maybe an epilogue about the MC only pretending he’s satisfied.
If it’s a tragedy, MC will choose Chisaki. This’ll lead to a snowballing catastrophe in which they ruin both their lives, even alienating the tomboy and lesbian, culminating in a lover’ suicide.
idk though. With the general tone of this manga, the second option seems too dark, but at the same time that’s the only direction I can see this story going.