Besides the obvious people are ****/people change/too much arguing/want different things eventually etc etc, I'd put forth the notion that as humans we're not actually
supposed to be around the same person for a great length of time. Just like your parents irritate the **** out of you after you've lived with them too long and you move out to make your own way in life... why is it really any different, besides intimacy and generation? It's just a theory I once heard someone say, I'm not sure if I agree with it or not. Sometimes I do (usually when I look back at my failed relationships!), but it sounds so negative and giving up-like. Maybe, maybe we just aren't meant to be with one person for so long.
I'm sure I'm maturing backwards. I was in long and intense relationships in my early teens (even when I was 8 actually, just didn't have sex ofc), grew out of parties and getting wicked drunk bro by 21, loved 60's music and hated, absolutely hated Dubstep. I was old before my time but the older I get the more ****** stoopid I become, with thought like the one above which seems to be leaning towards the typical attitude to relationships of that of a 17 year old boy. One night stands and dates are a ridiculous concept for me - that's not what I want at all, I'm just tired of relationships always failing so it seems this theory would sometimes fit.
Makes me wonder about undiagnosed mental illnesses, how many of us are actually aware of certain things happening around us that affect us in everyday life... ignorance is bliss kind of thing. Like there's just a part of content people's brains missing or something, the part that screams at them how god damn annoying other people are. It's probably like a person finding religion because they can't accept the thought of eternal nothingness after death, I'm calling everyone who is happy mentally ill or completely unaware of life...
...which is stupid. I'm not saying that at all actually. I thought it for a moment there but realised how silly it sounded. I'll post it anyway but any comments on that part in particular have been disclaimed already by this what that you have gone done reading now!
I am sad that I have lost so much and it still hurts.
edit:
I also wanted to say about the war and stuff. Our parent's/grandparent's generations were a lot more romantic than ours, and I think wars had a lot to do with it. Being sent away with no choice, food rations, no Skype or webcams just letters of poems and love and the fear of them dying. Adds to the bond imo. Of course many people cheated on their wives or husbands during this time but I think it's a big part of why so many couples in the generations above ours stayed together for 60 years or so. Different times, different attitudes, not as much mental illness in the collective consciousness