I told that to my then ex bf (same guy I still talk to sometimes; though recently we have spoken about getting back some day......long distance) years ago and he didn't seem too impressed. He said ''Oh ok'', treated it as a whatever topic and we started talking about something else. It wasn't till some time started passing by that he actually believed me but initially didn't. It's been now 6+ years later since losing it and yes I still remember the date. It was on a Jan 4, 2007 and I was 19 years old and 9 months.
Anyway, one time I got curious and decided to ask him what he thought when I first told him that on the 2nd week or so of dating and his reply was ''I thought you were lying, saying that to make yourself look good, then I found out it was true and loved you even more'' and then he describe it was his best relationship ever with me. Recently, he also added that when he told this to a couple of his friends (after I told him) at the time, none of them believed it either and basically told him that it was BS.
He started describing everything he loved about me and him being my first was just another plus to everything else he already liked. But wow, I was a little surprised on hearing that I was first viewed as a liar trying to lower her number.