Firstly, I am so sorry for your lost, it is the worst thing imaginable to lose your partner and best friend and the pain it causes is without measure.
After two years it is perfectly natural to feel like you are starting to be ready to move on and meet new people, there is absolutely nothing to feel guilty about, your wife loved you and she would want you to be happy and get back out there.
As for your new attractions, it is also completely normal for a person's tastes to change, to be curious and even to discover new things about yourself. My advice, don't put so much pressure on yourself to label yourself, and when you feel ready, go out and meet new people, start conversations and stay open, if you meet someone you like or are attracted to, and feel comfortable, give yourself permission to see where it goes without worrying so much about gender and what you call yourself.
Getting back out there is never easy, but try and give yourself a break and remember that the best way you can honour your wife's memory is to live a wonderful life, like she no doubt would want you to do.