I'm currently learning the usage of から and got some sample sentences with a similar meaning, but I can't wrap my head around why in one example から is omitted. If used, is it just giving more emphasis of it being the being, but not really necessary? Does it have something to do with the time?
Example Sentences:
来週は恋人と付き合ってから三年記念日です。
今日は、私と彼が付き合って一年記念日です。