I guess your biggest problem is you never made sex the important issue you should have done years ago and I expect you have suffered agonies of physical discomfort and frustration because you loved your wife and wanted to treat her like a lady!
First and foremost childbirth should not make sex more painful and, unless there was complications to the birth resulting in scar tissue that can sometimes be painful, the complete reverse is more often the case as giving birth does tend to give everything a good stretching - lots of husbands call their offspring "bighead" because they have trouble touching the sides afterwards and their wives hardly know their husbands are inside...
Enlightened women work hard on post-natal exercises in order to firm up those stretched muscles...
I speculate your wife's discomfort has more to do with not being aroused and well lubricated than childbirth!
Certainly treating sex as a chore and carrying it out standing in the bathroom is not really conducive to arousal or to the comfortable and gentle love-making that should be, both an expectation and a way of life to a happily married couple in their 50's...
The tone of your post does make me think both you and your wife have lived a somewhat sheltered life to be able to have lived for so long without comparing your own sex-lives with others and finding your own lacking and wondering why?
Certainly the first step you should consider is discussing this with your wife - clearly she is unaware how important this subject is for you. Having kids off your hands and having the whole house available as a love nest and not using it is something of a waste...
You want more sex; it is normal for sexual appetite to decline as age advances but many couples are having healthy sex lives into their seventies and beyond - often it is the man whose inclination disappears first leaving his partner wishing she could turn back the clock!
If you don't sort this out now you are likely to be frustrated and possibly increasingly upset or even bitter for at least another 20 years.
A male friend has rediscovered his sex-life in his mid-80's...
You probably need more sex; I am not saying a married man in his 50's shouldn't masturbate but I feel solitary masturbation should be reserved for emergencies when your wife cannot be with you to help and to be a part of the experience...
One partner having a low libido doesn't mean sex has to be curtailed and the other partner is doomed to suffer or forced to solitary masturbation: keeping your partner satisfied is one of those things being in love should be about, whether it is a joy or is treated as a chore!
Few people actually like cleaning drains or toilets and other chores, but they are equally necessary and dislike of doing them doesn't exclude a sense of pride and satisfaction at a job well done and an important contributioon to continuing domestic harmony and the smooth running of the household...
The other partner's sexual needs are at least equally as important!
It seems you and your wife haven't realised that good sex doesn't require penetration at all and for many women (and men) extended foreplay is the best sex ever!
I strongly suggest your wife has a gynae check-up to check for problems. She might also benefit from something like testosterone patches...
I also suggest you have some good sexual lube to hand.
I suggest you leave the pornography alone as it is both an addictive poison and unnecessary: if you need to look at porn to masturbate - you didn't need to masturbate...
If all else fails an affair might be the answer to your problem - but only after all has failed!
It is not unknown for someone in your wife's position to encourage an affair or visits to a prostitute or even to introduce a female into the family circle for the purpose of providing sex for her partner...
Good luck!
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