Gay Means Homosexual?!?!?

I came across quite a few articles about how the word gay came to mean homosexual and these articles caught my eye. To be totally honest I never even wondered about this. Without reading these articles at first I thought about how this came to be. So first I looked at the definition of gay.

1gay
adjective \'gā\
1 a : happily excited : merry 
  b : keenly alive and exuberant 
: having or inducing high spirits 
2 a : bright, lively 
  b : brilliant in color
3 : given to social pleasures; also : licentious 

I was hard pressed to find any entry that didn't include sexual orientation. So I added the about definition I found but left off the homosexual part. Just looking at the definition didn't say this word should be used to describe same sex attraction. So I was puzzled about how we commandeered this word for our own - that lead me to read the articles. Instead of writing about what was in the articles
I think I will just list some of them and let you read them yourselves.

How did "gay" come to mean "homosexual"?

How ‘Gay’ Came to Mean ‘Homosexual’

 How did the word gay come to mean homosexual?