Your original question was if you are the bad guy. I think the answer is yes if you allow any loving relationship to devolve without either trying to save it or communicating clearly what is changing and why. Respecting the relationship and the other person enough to either work on it or change it, even if it's on its way out, is just the loving thing to do. And if you treat a loved one, or even a former loved one, in a non-loving way, then, yes... bad guy. :/
Now, maybe you *have* gently communicated to her that you want your relationship with her to take on a more secondary form, and discussed what that could look like and what would work for you both. If so, kudos. I couldn't quite tell from the above posts.
Having your feelings change doesn't make you good or bad, its all in how you handle it and the level of compassion you show.
The major players. Me, 30ish bi female. Gia, girlfriend of 4+ years. Clay, boyfriend/dom. Davis, ex/friend/"it's complicated." Eddie, roommate & fwb.
The supporting cast. Eric, Gia's husband. Bee, Gia and Eric's toddler. Dexter, Gia's lover. Helen, Eric's lover. Izzy and Nikki, Clay's partners. Liam, Eddie's husband.