Wanting to move on from a long term relationship but unable to

[Darius]

Health issues that change a relationship can and do happen in long term relationships, even more so when you have such a large age span as yours does. This is when commitment to the relationship comes to the front. If the shoe had been on the other foot, what would his response to you have been and what would you have expected of him?
You said the new guy would leave you if he knew of your current relationship. Does that mean you would leave your partner and never tell the new guy he existed? If you tell him you are leaving your partner for him, would he still dump you?
Don't you suspect your partner already knows you are seeing other guys after 5 years without sex?

I know it's a lot of questions but it might help to face them.