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My blogger friend has decided to close her blog and I'm feeling a bit down about it.
Literal
Honorific-friend blogger-[polite-さん] [subject-が] blog closure [object-を] decide-[honorific passive-された] feeling-depressed-[somewhat-気味] [copula-です].
Blog-diary register, common mid-2000s personal blog phrasing. 決心された uses the passive/honorific form of 決心する to show polite respect toward the friend making the decision (not actual passivity). 凹み気味 combines 凹み (from 凹む 'to become depressed, feel down' — literally 'to cave in/become hollow') with the suffix ~気味 'feeling somewhat, with a trace of X.' さん after ブロガー is a polite/affectionate address — treating 'blogger' almost like a role or title.