From what you've said, he has no intention of leaving his wife.
That will very likely remain the case; even if your sexting escalates to physical cheating.
Which means .... He's got a life partner ...and someone on the side for flirtation, validation , stimulation, ego boost, illicit thrills, variety etc.
You, meanwhile, don't have a life partner and only have the scraps of a man who's not single.
He's still sharing his table, bed, home, holidays, family events, finances .... Life essentially with his wife. And will very likely continue to do so.
He has the loaf of bread. You have some crumbs
Get your own load of bread.
He's treating you very shittily, whether he means to or not (probably not, he's just being selfish and taking what he can take - because you're letting him take it) and you're treating yourself very shittily.
It's not easy to meet people but you can try your utmost. It's a numbers game. Every bit of emotional and sexual energy focused on a not free/available man like him; is distracting & subtracting from energy & focus towards you meeting a partner of your own; your loaf of bread.
You quote a favourite youtube of mine "I wouldn't share a pair of shoes, let alone a man".
Why "share"? There are other men out there.
(And it's not even really sharing; as I said, it's crumbs).
He's not sharing/taking crumbs from a woman. He's got a life partner, and a bit in the side too (even if it's not been physical). He's just happy to let you take crumbs.