Transition is a long process... maybe some people here on forums like this or youtube intentionally or unintentionally give the wrong impression, like it was just month or two and they went full-time and it was all fairytale and that was their transition. Its often the opposite, and transition usually takes a few years before you feel at peace with yourself in your new life. Going full-time can be quite stressful even when you are completely ready and you know it is exactly the right time to do it. Going full-time before you even feel ready can be a little overwhelming, to put it lightly.
How long to wait before going full-time very much depends from one person to another. Some can easily handle not being passable, some less, some don't. Some can go full-time before hormones, and some will wait two or three or more years and wait for the hormones to kick in. Some will have androgynous phase for a couple years, and some other wont. How will you be able to handle the changes is something only you know, and your therapist, if you have honest conversations with them.
Your main reason sounds a bit naive. You had a girlfriend like a few months ago, and it seems like that it wasnt such an unthinkable problem to have relationship back then. No matter how much would most of us like the transition to be quick and simple and be over with before you even blink, it's still a process... and it's not about the surgery, but rather to be able to move on with your life and live a life worth living.