<human>: Can you condense the text into three sentences or less?

I'm a 32 year old woman that is in a serious relationship with a 31 year old man.  We've been dating for just over a year and things are nearly perfect.  We've been living together for a few months and things have only gotten better since we got our place.  We have fun together, going out as well as just relaxing at home. He tells me he's happy and he loves me, takes great care of me, treats me very, very well, we have incredible sex...the whole package.

So...how come he's been sleeping with someone else? I don't know much about the relationship with her other than he was with her before we met, split from her before (or at least very early in our dating), and then started seeing her again. We talked about it when I found out about 6-7 months ago and he said it was just sex. He said that sex doesn't always hold an emotional attachment for him, sometimes, it's just sex. He said I was what he wanted.

My question is, particularly for men who might be able to shed some light on this, can you love someone, live with someone, eat, sleep, play, breathe with someone, have a fantastic sex life with someone, but also have unemotional, unattached sex with someone else?  And if you can do both, do you reach a point where you don't need the latter anymore and really let it go? I really want to understand so try not to judge me too harshly or call me stupid. Give me some honest feedback!
<bot>: in a great relationship, he slept with someone else and says it was just sex and there's nothing else there, and I want to know if this is really a possibility?