Mahsa's answer is good, but I'd like to point out one thing. 평생 doesn't mean forever but "for life", "throughout one's life", etc. "Forever" is most commonly 영원히 or 영원토록. There's also 영구히 and 영영. So 평생 친구 means "lifelong friend". 평생 교육 is "lifelong education", 평생의 일 "lifework", and 평생의 후회 "lifelong regret". 그녀는 평생(을) 독신으로 살았다 means "She lived her whole life unmarried", for example.

친하게지내자=> 친하게=friendly and 지내 is the stem of the verb 지내다 meaning to spend time doing something and 자 is let's 평친=> 평생+친구 = 평생 meaning for ever and 친구 is friend 콜= do you agree? ok? 친하게지내자 => let's be good friends for ever,ok? I think it's complete and correct : )

Just a comment. 콜 is originated from the poker term "call". To call is to match a bet or match a raise. A betting round ends when all active players have bet an equal amount or everyone folds to a player's bet or raise. If no opponents call a player's bet or raise, the player wins the pot. If someone ask you "~하자. 콜?", you can answer "콜!"