When my now wife and I first went out together the sex was great, adventurous and fun. From getting blowjobs while her parents and niece were in the car with us, sex in public places, handjobs on the side of the road, sex with someone sleeping next to us no more than a metre away and just sex in general almost everyday. She would let me slide my dick between her arse cheeks, or her breasts to get myself off and then take my load in her mouth and I was able to finger her or give her oral quite a bit.
10+ years down the line, we're married, a little larger, have three kids and the extent of our sex is a little missionary here and there. She doesn't like me fingering her any more, she doesn't like oral either way and all in all it's quite boring.
I'm a very sexual person and quite often find myself looking at other girls and porn, not only lusting after them, but reminiscing about old times and wishing my wife was the same as what she was back in the days.