It's sad reading that letter. I hope he gets the support he needs and manages to find peace within himself. The fact he thinks he has to retire from the game he loves before he can come out is a shocking indictment on the game.
The problem for the first player is that it will make the news for a few days, and he will, get alot of attention, not all bad attention, but from his point of view, I guess, he is asking himself why should be should be the 'Bosman'. People growing up in the 80s and 90s, were actively taught to be homophobic. And yet as times have changed, even many of those have fundamentally changed their opinion and views on the subject. And those who haven't just come across as deeply ignorant and out of touch. But most millennials and GenZ have had a very different cultural education.
There will be a minority of people who will abuse him, and he may get the most, vs others that come after him, but I think it's no more than other persecuted minorities get in UK like BAME or Muslim players. I suspect the vast majority of other players as millennials will be very supportive, and think it's not a big deal. Im also sure their clubs and The Premier League itself would be hugely supportive, and ensure any provable abuse was dealt with.
Perhaps 10 gay footballers can find each other and all come out together. I think that would be the best way to do it. Once the first group come out, and hopefully many others quickly follow, it becomes 'normal', just like in many other parts of society like in hospitals, in the office, or in the entertainment industry etc.