Quick take on Monogamy

today I had a date with a guy, and everything was going perfect until I decided to go to the point and asked him if he wanted to go back to my apartment and fuck. Normally that’s a sure yes when I date guys, but this time he answered "no"!
first, I thought that he was still sexually confused, but then he explained to me that he was engaged!
I felt sick hearing those words. I don’t believe in monogamy but I’m still no one’s “other”.
He started to tell me his insecurities of being with just one person and other things associated with marriage, even though I didn’t ask. But I realized he was messed up, he was more like me than he realized, and decided to fall in the unreal idea of monogamy.
I thought his insecurities were well fundamented. My ideology is that humans are not supposed to be monogamous, having said that, if you decide to engage in monogamy, you have to be loyal to your partner and own your mistake.
I don’t respect guys like the one I dated. I can respect someone loyal to his word, I can respect someone that decides to never be loyal to anyone and doesn’t engage in a relationship, but guys that engage in a relationship even though they aren’t sure about being loyal to just one person…. I can’t respect that. Makes me sick.
The guy I dated also explained to me that he engaged because he wanted kids. That’s a problem with our society, thinking that a kid can only be raised in a home with two married parents, even though there are countless cases where that’s not the case.
At the end of the day I lost my entire afternoon and I got no trade, but at least I got to analyze the insecurities of a person before marriage.