SuperFlan,
I am the guy that everybody poked at in school: Fat/Fatty, 4-eyes, book boy, babble-babble, you named it (I looked at the old photos, I was not fat by any world standards).
I also was in your step-daughter's seat.
But I loved my step-dad to death, and respected him. Even when I saw him giving his everything to his boys....
I think if you want to be around your son and your wife, you have to include your step-daughter:
-you are NOT her father
-you will never (in her eyes) be her father
-since we clear this out of the way, you need to decide what you want to be to her, and be constant about it
-she will grow up at some point. she will see who was the "heart father"
Now, if you drive/ride home, if let's say it's 20 minutes, take the long way for the 40-45 minutes, to blow off some steam...
Like others said, take care of yourself physically, have at least one hobby (you can also share that with the 2 curious kids).
Groom yourself, like MRS. Supreflan is a super-model on the first date. She will appreciate the attention.
You will appreciate feeling better about yourself.
If other ladies will give you attention, well MRS Superflan will get into cougar mode and "protect" her conquest: YOU!
DO NOT LET THE STEAM ACCUMULATE! It will only blow....
So find your own corner/activity/hobby/circle of friends (choose them based on what you want to be)
...and don't listen to the ones that tell you "just pick yourself by the laces/boots"...
You wear flip-flops and them not
Bon Chance , Mon Ami! A bientot. Tout va bien!
P.S. learn as much IT as you can, and move to sys admin/engineer