If you feel that not coming out will make you more happy, than that's ok nobody has to know. But a lot of people find that when they do come out there is a huge burden lifted of their shoulders. But maybe for you it is more comfortable to stay closeted, and that is completely ok.
I don't know. I'm instinctively more comfortable keeping my social and my family life separate. I know it's a terrible thought, but it's almost like I've always tried to hold on to some sort of "purity" with my family life. Some sort of desperate vice-grip on my childhood innocence. I'm always having to put on a mask. Always having to play a role.
That's fine, as far as it goes, and yes, the decision (and it is a decision) to remain closeted is entirely your own. As long as you have worked out all the angles and have come to the firm conclusion that this is right for you, who are we to say otherwise? However, you need to acknowledge that much of what being closeted means is fear and avoidance of a difficult conversation. You need to factor that also into your calculations. Eventually, you may find yourself in a relationship, possibly with someone who is out completely. Your being closeted will make your relationship difficult, to say the very least. When it comes to avoidance, we humans are incredibly creative at finding excuses and rationalizations. By all means, this is your decision, but examine your motives carefully, living in fear is not the best way to live, or love.
A lot of people, myself included at one point, don't believe you should "have" to come out. Why make such a fanfare over something that shouldn't be a big deal to other people? Straight people don't feel the need to tell people they're straight. Well first things there, straight people do tell people they're straight, constantly. I don't think it's possible to get through a day without hearing about how straight the world is. But anyway, though this sounds odd, to get to the stage where you don't worry about other people knowing, you have to come out first. I'm now at the stage that I just casually mention, if it comes up, something that relates to being gay (having a husband, etc). I can do that without missing a beat, without a second thought. In fact it actually surprises me when I hear about people that don't know I'm gay. To get to that stage though I had to come out to the people that mattered. The people that are going to ask me about my love life, about my relationships, the ones that are going to be in my life for years or already have been for years. I know it sounds stupid, but to get to the stage where you don't "have" to come out, you have to come out first. You shouldn't let fear control your life.