if you take everything in a 'realism' and realism only take on this ending, then sure its good, but for the purposes of the actual story, we spent the entire time in this highschool, exploring these characters, with plenty of room to atleast subtly foreshadow that taichi may possibly show bisexual feelings, and we really didnt explore that(which is a shame, cause the mangaka is a good writer). yes in real life, it is possible he just never realized it in HS, but for the purposes of a story that mainly focuses on that setting, you cant have none of it and then BAM, time skip, dude realized he was bi, got with touma, the end! its rushed, no matter how you look at it
but other than that, im fine with everything. besides for the fact that highschool relationships dont tend to last, we also saw that futaba actually was scared of losing taichi to touma even in High school, so i can totally see how these feelings would continue, seeing touma and taichi grow closer, and how they would eventually break up, and even why they wouldnt see each other again for so long.
as far as im aware, im just gonna take this end as if i was spoiled, and im just waiting for some novel or side story to fill in the context of the time skip to show how it actually happens. other than that, i was surprised by the gay, and had mixed feelings initially, but eh, it was a solid ride