The president of CBS' entertainment department spoiled already before the season began that Vanessa's character was a lesbian, and that the viewers would understand that as the season progresses, so this is not some sudden random idea that the writers came up with.
I've got nothing against God, it's his fanclub I can't stand

It wouldn't bother me either, I like her either way,
but I also don't remember anyone talking about her being gay or bi, where did that come from anyway?

Well so far it hasn't come out that her character is gay - unless I missed her saying something about it, but I haven't missed an episode. It wouldn't bother me if she was gay or bi, I live in New Orleans and we are a very diverse and acceptable city.

A woman that I work with was married to her husband for over 20 years with 3 kids, she divorced him because he was on drugs and could not take it any longer, soon after she started dating another woman. I certainly don't know how that works.

I don't know that is true. My best friend from high school had been in long relationships with both men and women.

You don't start dating women because you had terrible experiences with men, that's not how it works. She was always attracted to women, but she hadn't figured it out or accepted it yet back then when she married her ex-husband.
I've got nothing against God, it's his fanclub I can't stand

She had conversations with both Pride and Percy about how she used to live in New Orleans, but she left because her (now ex)husband ran off with a substantial amount of FEMA money that was supposed to be used to rebuild after Hurricane Katrina. Considering that was 11 years ago, I think it's safe to assume that the fallout from her marriage is at least part of the reason why she started being with women.

They didn't go into specific details about her past other than she had a lesbians relationship that started up about ten years ago. Before that it's still a mystery.