。
Please, just tell me the truth.
Literal
I-ask-[because-から] true thing [object-を] tell-give-me.
頼むから ('because I'm asking [you]') is an emphatic preface used to plead — 'please, I'm begging you.' から here gives the reason for the speaker's plea. 本当のこと ('the true thing / the truth') is the everyday way to say 'the truth' in Japanese.