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I really disagree with the idea that Will would be ok with liking boys if he didn't love Mike and that Mike would be ok with loving Will if he wasn't a boy. Maybe it's a snappy sounding post but it's also just...not true? Acting like Mike is The One™ with internalised homophobia and that Will is completely chill with his sexuality completely goes against canon.
Did you guys forget the bullying and abuse Will experienced because people thought he was gay? The van scene? Canonically, the only thing stopping Will from feeling like a mistake is the fact that he loves Mike. Because Mike makes him feel like he's not a mistake. He makes Will feel like he's better for being different. If being gay is be unnatural and bad, how can his love for Mike be so beautiful?
Will is becoming ok with his sexuality because he loves Mike, not in spite of it.