Konnichiwa Elizabeth-san!
"jibun no koto o kangaetekureteiru hito ga iru to iuno wa ureshiikotodesune."
The most simple wording is "I'm happy because I'm not lonely". This is the most important point on that sentence.
And different wording ...
"I'm happy because I have warm family"
or
"I'm happy because I have a friend who like me"
or
"I'm happy because I have boyfriend(girlfriend) who love me".
and etc...
All sentences has the same meaning, "I'm not lonely". But why the Japanese say so long as "it's a happy thing that I have someone who is thinking me"? Why the Japanese don't say more directly? Because the Japanese dislike a direct saying. An instance, the Japanese say "I like you" but not "I love you" to boyfriend(girlfriend).
Sorry, I made a digression. You can translate in various, but the most important point on that sentence is "I'm happy because I'm not lonely".
Of course you can substitute the first person for the second person as "You are happy because you are not lonely".
But pay attention to my saying because I don't know all sentences you have, and my saying is a generalization.
Sorry, if I make an error.
NANGI