Who are you to say that all of that was build up to a relationship? How do you know that all of the previous interactions between Blake and Yang were build up to relationship? What if it started out as just as interactions between friends that wasn't supposed to give hints at anything romantic?
My whole entire issues with Blake and Yang is that I feel it was not handled well in the story. It felt like an S-Support in Fire Emblem where some units casually talking with one another, and the for some reason they decide to get married because...well, just because. It had absolutely to do with the fact the relationship is a lesbian couple. If the writers had given more depth, more development, and more reasons as to why Blake and Yang like each other, then I wouldn't have little to no issues with it.
And here's the thing, this is all my opinion. I'm not forcing this belief on anyone else. If you think Bumblebee is a good ship, then more power to you. I just think it was handled poorly in the writing and felt like fanservice, not because it was lesbian shipping, despite what Gwen will try to tell you.
Being upfront and honest, if labeling someone a homophobe is your reaction to a differing opinion on a ship, I can't take you seriously.