Hi Ashiriko,
By starting and following the process, I mean you will need to be patient because transitioning will need time and process (both in term of explanation to 'significant others' (SO), and in term of your transitioning itself.) There is no short cut in transitioning. This process might need months or years depending on different individual situations. If you need something long enough, then you can be sure that you really need it.
So if you spend sometimes (perhaps you have spent your whole life already) to consider until being 100% sure in your mind that you want the the transition, you don't need to delay your 1st day and the rest of your life.
In explaining to your SO (if you don't want to lose them), you may need to do it step by step. Be honest to them, and respect your true self. When explaining, you can not tell them everything in the first time, you may have to tell them the big picture about who you really are, why you have not told her (or them) before. They will be shocked enough, then give them sometimes to think about it, and tell them little more by little more.
In my case, it is complicated. I live with my wife hometown with her huge extended family (in Thailand) even though I am from small, urban, and independent family. I came out to her (just that I want to become a woman, but I still love her. That's it) but decided to take hormones secretly . Having her loving husband as a transgender woman could be okay for her but not her family. So I am in a big decision and action of my life.
In the next 2-3 months, my feminine side will obviously show off (breasts, face shape, and hips), I plan to leave her, and start my life all over again. I know that it is hurting her a lot. I may come back to see her and my daughter when I look more female, and see if they can accept me or not. If they can't, it would be easier for me to permanently leave them.
(to be continued)