手前 meaning in this sentence

「手伝うって言った手前、ちゃんとやらないと。」Context: a person promised to help a girl with something and is now telling that to a friend.

The rest of the sentence is no problem, but I can't figure out what the meaning of that 手前 is exactly. I'm guessing it's something like "since i'm in a position of saying that i'll help...", but I'm not exactly sure.
I searched around the dictionary for it, but I found some explanation about it which I can't figure out either - 「人に対する自分の立場・体裁」, also 「他人に対する，自分の立場。面目。体裁。「友人の―知らないとは言えない」「力になろうと言った―断れない」」.

If anyone could also clarify what 他人に対する，自分の立場 and 人に対する自分の立場 mean, I would appreciate it.

Your translation stands correct in my experience.

"Since I promised to help, I gotta do it right" seems more clean though

「人に対する自分の立場・体裁」 「友人の―知らないとは言えない」 roughly stands for "a position assumed towards someone else."


手前 : てまえ【手前】の英語・英訳 - 和英辞書 - goo辞書

約束した手前行かないわけにはいかない
Since I've promised, I have to go.

Thanks, I appreciate it.