Extramarital affairs

What's up with this constitution of marriage tho?

I thought it's supposed to be a "for better for worst" kind of union? A union of till death do us part? A union where you are sure you want to spend the rest of your life, both happy and sad moments together? Was it not made to be sacred union? But why is the sanctity of marriage now lost? Why is it so easy to see married people having extramarital affairs and annoyingly it is now seeming like the norm of the day?
The most annoying part is, initially we all thought it was just the married men who cheated on their wives but mehnnn have you seen the statistics of married women who cheat?? It has gotten to the extent that some men even prefer carrying that act of cheating with married women because they feel it's better than having to deal with young ladies. Imagine? It's just so alarming and disgusting. Here's an experience I had with a married man quite recently.

So I was at my aunts house and her husband's friend came visiting that morning, I was relocking my dread outside, cause the guy who does the dread maintenance for my aunt came that morning. So while we were at it, the man came and there was an exchange of pleasantries, I greeted the man as well but I didn't really pay attention to him. After two days, while I was going somewhere in the morning I met the man and he called me, he introduced himself, saying he was my uncles friend that came two days back and he asked for my number, which I gave him. That evening baba messaged me and started the whole I love you talk, telling me he doesn't usually do this but he's just attracted to me, all this his plenty talk, his wife and children were his profile pictures ooh! I was just reading his messages in amazement, so I asked if he wasn't married, he boldly told me he was married and even asked if I didn't see his family's picture on his profile picture? I was shocked at his boldness and guts guyyy... It was like a normal thing to him. And he was casually saying it like his being married shouldn't be an issue for me, now remember he said he doesn't usually do such? Well he dated my cousin who stayed there some years back and he just wanted to do it again.

I'm sure a lot of girls have faced the whole married men asking them out in one way or the other but then again even men face such encounters with married women as well. My major cause of conflict and concern is why? Why is this extramarital affair thing gradually becoming a normal way of life. And one yeye man /woman will tell you I need to explore other people I can't keep tasting the same thing always. Really? Wasn't it part of what you said while making your wedding vows? "to forsake all other women/men and to cliff to your partner alone"? Where did this constitution of marriage go wrong?