I've been full time for two years, and 'transitioning' for around 10 years in one way or another. I've lost very few friends, and none of my immediate family. I have a full time job, a stable life, and all my needs are met. I have no regrets at all about transition, and to this day I'm happy I did it and feel that it's resolved my dysphoria.
However, I still have 'second thoughts'.
I'm just the kind of person that likes to plan things out really well, and avoid unnecessary risk. I worry about things (not just transition). And to be honest even though transition has gone really well there are still things that worry me about it every once and a while. At night when I'm half awake the worries come like "am I harming my body by taking these hormones?", "when my ex-wife finally moves out will I become overly depressed and lonely", "when I have surgery in three months will I have the strength to make it through the hard times?" These and more worries.
Transition for me has really been about being honest with myself - admitting to myself what my true fears are and what really makes me happy. It's a difficult thing, and I look at some people who just seem to go through this as though it's a dream come true or whatever and as though they never had any doubts and I definitely don't completely relate. I worried a lot about the impact on relationships, and my health, and all that - and yet I also honestly knew that I've always wanted this; always known I wasn't and never wanted to be a guy. I still don't want to be a guy. I never want to go back - but that doesn't mean I don't worry. I do sometimes even though I know all this stuff and I've already come so far!
As others have said, you know what you need and want deep down - and who you are and how you feel inside. This is what should be the thing that guides you to move forward or not.
I personally look at my doubt as a sign of honesty within myself. "Checking in" with myself to make sure I'm being honest with myself and not doing things for the wrong reason. For others this might work, but I've come to see my 'second thoughts' and my doubts as a way of staying grounded throughout this very difficult (and yet rewarding) process.
I have found strength in vulnerability. Maybe you will too? You're not alone.