I feel a bit mean saying this.
BIL who was 30 at the time, met a woman and declared his love for her after about 2 days. Engaged 2 weeks later, prattling on all over social media about how she’s his angel and saviour, so in love, blah blah. He said to us the day before he proposed that he was asking her to marry him and we said “Um isn’t 2 weeks a bit soon?”. Cue MASSIVE man tantrum, shouts of “I’ll show you all, This is true love, fuck you all”. After 4 weeks she found out she was pregnant - apparently conceived the night they met! Waxed lyrical about “See! see! I told you it was true love” - as much as I wanted to I didn’t point out that failing to use a condom is not a sign two people are meant to be.
We did express our worries that it was all happening so soon, and to not get ahead of themselves, get to know each other properly etc. But he was so defiant that she was his true love and Everything Was Great. My weird in laws scolded us for not being super duper supportive and agreed with BIL that it was True Love.
By month 4 of the pregnancy they absolutely despised each other. Screaming matches, tears on the phone, the lot. I grew close to her (he has good taste, she is lovely!) and turns out he very much misrepresented himself to her in the early days so she got swept away in the romance.
Anyway by the time the baby was 3 months old they split up and have had the most toxic relationship ever since. Which is awful for their lovely DD - who is now 9. And the family have been real pillars of support to them. I’m still close to her and we often meet up with the kids, they’ve both moved on with other people but my good they really can’t stand each other.
I’ve never said “I told you so” but it’s hard not to when he bangs in about what a stupid cow she is and how she’s thick/rude/stupid. I have said on occasion however that he’s just gonna have to square it with himself that, if you have a baby with someone you barely know, you can’t be surprised when it doesn’t all turn out peachy.