Please help me check my conclusion paragraph~Thank you!

In conclusion, it is more advisable for people to maintain the friendships with a small number of people over long period of time since it encourages people them to understand each other better, which could share everything to friends. What's more, it helps people make lifetime real friends to whom they can show their real face express their true character. The ability to maintain the friendships over a long period of time can therefore be regarded as  more important for the  critical to happiness.

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I am really confused about how to write the last paragraph of an essay, please help me check the grammar and help me change some words(some words might be too simple to be in an essay.).
Thank you so much!!