Not at all. Just my usual nightcap. It's nice to have company once in a while.

Literal

Not-mind [emphatic-よ]. Usual [possessive-の] night-drink [copula-です]. Occasionally partner [subject-が] exist [nominalizer-の][also-も] good thing [probably-でしょう].

構いません 'I don't mind, no problem.' 夜酒 'nightcap, evening drink.' パートナー 'partner' — a loanword used broadly. たまには 'once in a while.' いいものでしょう 'it must be nice' — ものでしょう adds a reflective, philosophical tone. Warm, mature bar conversation.