How do you manage your emotions without being fake? How do you keep it inside without later exploding on someone?

That can be hard. I think sometimes we suppress/hide parts of our true selves due to others reactions or labeling of us.. Too emotional, too this or that or not enough of this, etc...

Being cognizant of our inner selves is key. Trying to be more aware of our [b]re[/b]actions and learning to breathe and hesitate before over reacting. Finding a way to let it out and express it through means of exercise or writing or some such helps too.

Good questions. I spent most of my life ignoring my emotions. That deadened me somewhat, though I did it believing it was helpful. Now I'm having to learn to acknowledge my feelings as a starting point, not ignoring them, then gradually I guess I will learn to manage them better. I think journalling can help, to capture feelings you have no-one to share with, that shouldn't be bottled-up.

I talk things through with my dog, she's a great listener

I react appropriately with whoever is deserving of it... I find masking those emotions is "fake".

If things aren't good, they'll know. If they are, they'll know. I like to confront problems and move on.

Alcohol

I can't manage my emotion. People see me and said "why you look so sad?"...

I don't know how to explain it really to someone who can't. Just kinda learnwd or grown to be able to compartmentalize the anger until able to focus it into work or direct it at the culprit when it isn't disruptive to what needs to be done. Gotten pretty good at in as I grown older.
I'm not trying to say I'm better or anything. It's a strength that comes at a cost, it also kinda results in being seemingly cold and stand offish in other life facets.