Verified answer

まるで is an adverb usually accompanied by negative expression, meaning "almost/quite/totally/completely"

まるで 解らない I have no idea.　まるで ダメだ It (or person is) is awful/hopeless

Or it has another meaning "as if/ just like..."　

まるで 逆だ That's almost opposite. まるで 別人のようだった x seemed like a total stranger

まるで 寂しいです sounds very "new" to me, but as Tom says it could mean ”I'm quite/totally/completely lonely”

*We don't write ”丸で”

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not quite a good sentence but I'd say "totally lonely."