kudos to you, Mr Fixit. You've asked enough questions to keep me writing for the whole weekend.
1. Is it possible to be dominant in a relationship, but not in life?
No. You can't "be" dominant sometimes and not others. Because it is a trait. You can put ot on, like a mask or a costume, and then take it off again, though.
Dylan said: you gotta serve somebody. I think this is true.
Shakespeare said: we are merely players. This is true too.

If you have it in you to "be" dominant, it signifies a self-discipline first. I said that.

2. If you are dominant in all aspects of your life, are you automatically an asshole?
I think that if you take your self-discipline and the ability to carry social momentum to be a signal (to you) that you can and should try to control every aspect of your life...that will kill you, or at least make you very very unhappy. I was a supervisor for a number of years, in a trade, and nothing makes people act up, and deliberately thwart you like the sense that you are trying to "control" them.
I may be naive, hell I know I am, but I have learned the hard way that consensual teamwork and commitment are a lot less tiring.

Last thing: And this is with my heart on my sleeve:
When you meet a girl's parents, you have nothing to fear if you love her and you are not afraid to let them see that. If you are not sure and you try and fake it, her mother will know.
The self-control you need to take control another and let them experience something they need at your hand leaves no room for self-doubt. Same with "life." If you have doubt someone will find it and neutralize your momentum.
In some ways what I've written here is like self-help. All recipe, no stove. It takes a lifetime to get to a place where you can dominate lovingly and not from anger or hate. Ain't no book can make you a better you if you can't stand to look in the mirror.

No t"all weekend" but still too much. Sorry.