Sorry but the person who wrote the letter sounds like an utter knob.
"When I say, I am a loyal customer I mean you have had me for the better part of my adult life, hook, line and sinker. I will spend the extra $2.50 for a cup of your coffee. When I worked in Hoboken I would walk an extra three blocks for your coffee, walking past a Dunkin Donuts, Panera, Macdonalds and two bodegas to purchase from you. Every morning I drink my coffee out of one of your ceramic mugs and I have for years. A dozen of them line my shelves, (even the poorly conceived ?Father?s Day? argyle mugs from 2005 that have metal bottoms which means I can?t pop it in the microwave to reheat) I only buy Starbucks for my home consuption. When you roll out a new product, I flock to your nearest location like a moth to a flame. I mourned the loss of the Chantico and I even rushed out to try that banana mocha abomination (a match made in hell) blindly following your suggestions like a lemming. "
I imagine the guy was forever going on about his love life and his co-workers got sick of it and told him so. Because he was gay it suddenly becomes "homophobia". If it was a straight man talking about all his conquests in front of female colleagues it'd be a different story.
If they used homophobic slurs, discipline them, because that isn't acceptable. But gay people shouldn't expect special treatment on the grounds that they are gay.