Mike and Will's love story is intended to be a surprise not only for the audience but also for Henry.
Will and Mike's love for each other is a statistical improbability that should not exist, yet it does.
It is rather obvious that if the writers are going to portray Will and Mike as being in love, it would contradict Henry's speech about conformity:
"... a cruel reality dictated by made-up rules. Seconds, minutes, hours, days, weeks, months, years, decades. Each life a faded, lesser copy of the one before. Wake up, eat, work, sleep, reproduce, and die. Everyone is just waiting. Waiting for it all to end"
I believe that not only the audience will be shocked by Mike returning Will's feelings, but Henry will be taken aback as well: two boys deciding to forge their own path and be together challenges Henry's worldview. When queer love becomes real and undeniable, it creates a crack in Vecna's illusion.
Yes, Henry potentially has the ability to see into the future, but here he may be reading Will's mind and concluding: "You are just like me. Misunderstood. Rejected."
Given that this is about Will's thoughts, after Mike's love confession and the "my life started the day we found you in the woods" nonsense, we know he feels hopeless and crushed. Henry's certainty here depends on the assumption that Will has no true hope for love or belonging - because from Will's perspective, he doesn't believe his love will ever be reciprocated.
I am more confident in this "plot twist" route after reading the Watchmen comic. Dr. Manhattan also views the universe as deterministic and pointless, leading him to abandon humanity and not want to prevent nuclear destruction.
However, he changes his mind upon discovering that Laurie, his ex-girlfriend, is the daughter of a man her mother and she despise. She says she's just a product of a messy, human mistake, but to Dr. Manhattan, this realization becomes proof that Laurie's existence is an improbable miracle of love and chance, rekindling his sense of wonder.
To Henry, the fact that Will and Mike love each other is a statistical improbability that should not exist, yet it does.
Their relationship demonstrates that love does not arise from conformity (like Eleven and Mike's relationship) but rather from an unexpected, stigmatized queer bond. This directly challenges Henry's claim that everything reduces to predictable cycles. I'm not suggesting that he will suddenly change his mind and embrace peace in the name of gay love, but it is clear that he will be shaken and destabilized because his worldview has been challenged by something as delicate yet undeniable as love.
In this way, Will and Mike's queer love becomes an improbable miracle of courage and connection that disrupts Henry's nihilism.
