No Balance Ever! Relationships don't work like that even when you are monogamous. 50/50 is a myth like a picket fence. Most relationships are some imbalance of one thing or another maybe its 70/30 on the income and 10/90 on emotional support.
You are not being honest with yourself if you are OK with an open relationship and at the same time say you are totally satisfied. If both of you were totally satisfied you wouldn't need outside stimulation. The whole concept of an open relationship is that you both agree each other can not satisfy ALL your sexual desires. 1st guy or 101st guy dose not change this. Sewing your wild oats is a cop out after being together so long already. Crystal Meth wasn't around much when I was younger, so should I start now so I can experience what I missed out on? We all make choices regardless of age.
I know a lot of couples that have been in relationships a long time. About 50 percent are open and 50 closed. If I had to generalize, the open relationships tend to have more drama, jealousy and shorter lifespan then the monogamous ones do.
If that continues into mid life it starts to look pathetic. It gets uncomfortable to go out with older couples who have open relationships because they always seem to be on the hunt. Instead of developing other parts of their life and solid friendships they spend most of their free looking for the next trick. And as you get older and older, there are less and less takers making you look more and more desperate. These are the guys I see in some dive bar at 12:00 in the afternoon drunk half blind annoying the 20 year old stripper then goes how to their "understanding lover". Who by that point wont pick them up at the bar anymore.
It seems more often then not, of the couples that started an open relationship after they were together for a number of years, is just a way of one partner to make an easier exit then if they were exclusive. Even if they truly don't plan on that, it just happens when one or the other suddenly meets someone where it moves for just sex to emotional attachment.
Then it's by by relationship because its not like they will be loosing anything special or intimate that they don't have with the new guy. " Oops, sorry, we fell in love, it just happened."
Of course there are always exceptions, but I only know one couple that have pulled off the open relationship thing in a healthy way without coming across as predators on the next Chris Hanson Show on NBC.
Since you are questioning who is getting more sex outside the relationship, you don't sound like your headed to happy town. And, since your other half seems to engage in A LOT more action, it dose not sound like he is satisfied with you either. You are on the road to just roommates.
Harsh I know, but you asked.