So, Is it necessary to be socialize ?
Life would be difficult, even impossible, living completely alone. There is a reason that the sangha is considered one of the three jewels in buddhism.
If it is, Why buddha said, go to a forest to meditate ? Get a free and quite time ?
Yes. Your understanding is on point. Withdrawing into reflection is helpful for developing a buddhist practice from time to time.
If it isn't How do I recognize those thoughts ? (If we have no reason to get those feelings, we might think we haven't those thoughts)
Perhaps you are right, one could possibly avoid developing aversion in solitude. However, to a larger extent, it seems to have a tendency to foster a feeling of alienation. Too much time alone may make us less accustomed to relate to others, even though we may have good intentions.
In the noble eightfold path, right effort isn't just about preventing aversion to take a hold of us. It is also about developing skills that we may not have right now. Prosocial virtues, such as the brahmaviharas is most likely impossible to cultivate in complete solitude.
From Magga-vibhanga Sutta:
"And what, monks, is right effort? (i) There is the case where a monk generates desire, endeavors, activates persistence, upholds & exerts his intent for the sake of the non-arising of evil, unskillful qualities that have not yet arisen. (ii) He generates desire, endeavors, activates persistence, upholds & exerts his intent for the sake of the abandonment of evil, unskillful qualities that have arisen. (iii) He generates desire, endeavors, activates persistence, upholds & exerts his intent for the sake of the arising of skillful qualities that have not yet arisen. (iv) He generates desire, endeavors, activates persistence, upholds & exerts his intent for the maintenance, non-confusion, increase, plenitude, development, & culmination of skillful qualities that have arisen: This, monks, is called right effort.
Or should I not think about that ? (Being social or not being social is out of my control ?)
It is likely within your control, and i believe it is a form of control that is beneficial, and not the clinging/grasping type of control.