In the manga, Mob's focus is mainly on his psychic abilities and personal growth rather than having a romantic relationship. So, no girlfriend for him.
In some comic storylines, Loki does have a girlfriend. But it depends on the specific comic run and version of the character. Sometimes these relationships are short-lived or complex.
Yes. The conflicts between Sanji and Luffy in the manga often stem from complex circumstances and character developments that drive the narrative forward.
As of now, Sanji is very much alive in the One Piece manga. The story keeps unfolding with him as a vital part of the plot. The author hasn't written his death yet.
Well, you could start by joining clubs or activities you enjoy. That way, you'll meet girls with similar interests. Also, be confident but not cocky, and always be a good listener.