Is it easy to maintain serious relationship?

Any one can make casual relation to any one very easily but to make serious relation with some one is very tough and to maintain it, it's even tougher than that.

Why people afraid in committing?

There can be two reasons. One is: they don’t want to show their relation to world or they are just passing time. Another is: they are not ready to hear rejection from his/her love one.

Does having sex before marriage valid or not, when you are not sure that your gf/bf is your destination?

As per my point of view, if you love some one and he/she is insisting you for sex, and yet it’s not fully finalized that you both are going to marry then you should wait for marriage. After all it’s your individual decision, what you want to do. But take care if you are going for sex before marriage.