I suggested a temporary tank to go along with my earlier suggestion of doing a fishless cycle on the 10G. It would be silly for me to suggest removing the betta immediately and then in the same breath suggesting that he not go into the 10G without it being cycled. Hence the suggestion to get a cheap temporary tank. I read your post, I think you just misunderstood my reply.
Carpenter 547, goldfish and bettas have completely different needs and are adapted to live in completely different environments. Goldfish are from cold waters with high oxygen content and do best in tanks with a decent current running through them for aeration. The filtration the pleco and the goldfish require would make the tank very uncomfortable for the betta, which is adapted to live in a still water environment. Goldfish and plecos do best with tank temperatures of the mid 60s to low 70s, too cold for a betta to function well at all. Bettas live in still, low oxygen, warm water environments--warming the tank to suit the betta is not an option because warm water does not retain oxygen as efficiently as cold water. Warmer water conditions would put chronic stress on the goldfish that would lead to eventual health problems. If he has a 10G he can use to house the betta, there is no reason to subject it to conditions that are unsuitable for it.
Also, interaction with humans is not a substitute for interaction with one's own species--that might work with some domesticated mammals like dogs, for instance, but not for fish. We can't very well swim with them and give them goldie-nuzzles, rofl.
while i don't disagree at all there are a few things to consider.
aeration has little to do with the amount of current but rather water temp and water saturation with other material *salt minerals etc* and surface area.
fancy gold fish like he has prefer a slow current since they are so disfigured and most of them prefer warmer temperatures not as warm as a betta likes but still warmer and can deffinetly tollerate betta temperatures on the low end.
bettas don't crave interaction with thier own species infact much like our own species they only want the woman for one thing and then want her gone. goldfish crave companionship and will accept it from any thing that tollerates them even people there is a video of a goldfish being petted by owner.
as far as health normal and expectancy the op is keeping 2 of the most inbreed deformed fish on the market so as i stated in my post as long as the op knows what is healthy and what isn't healthy what is and isn't stressed then there is no problem.
there is nothing natural about our hobby period. we take the place of god or mother nature depending on your beliefs in this hobby. i live in a desert in california and with in 50 i have fresh brackish tropical subtropical together *seperate tanks*
so again i don't disagree that a seperate tank is textbook best i maintain that if it is working don't worry. especially with the selected man made species the tank is stocked with. if these were wild caught fish it would be different but both fish have been made and maintained in any thing but ideal natural conditions *no slight to you op i am sure your fish keeping is top notch* for thier whole life thusfar.
animal husbandry means we enter into a bond with the animals we are keeping agreeing to maintain them in the best conditions we can with thier health as our main concern.
go forth and subdue the world doesn't mean kick it till it obeys.