どうせ、時間に関わらず、俺が先に来てなかったら、さっさとネカフェへ行く腹積もりだったんだろう。

、、、。

Honestly, regardless of the time, if I hadn't gotten here first, you were probably planning to just head straight to the net café.

Literal

Anyway, time [regardless-に関わらず], I [subj-が] first [come-て-negative-てなかったら], quickly net-cafe [to-へ] go intention [copula-だった] [probably-んだろう].

に関わらず '(irrespective of / regardless of)' is a formal set phrase. ネカフェ is a slang abbreviation for インターネットカフェ 'internet café,' common in spoken Japanese. 腹積もり (literally 'stomach reckoning') is an idiom for 'inner intention / private plan,' often something not openly declared. ~んだろう is the masculine-leaning hedged ending '(that's) probably what it was.'