First of all, you have nothing to be ashamed or embarrassed about. You’re not the one paying women to jizz into.
Second, he will be using them every time he’s away.
Third, you having health issues is no excuse for him to buy sex from other women or to sleep with other women or even entertain other women. He’s either in a committed relationship with you, in sickness and in health, or he’s not. That’s what a partnership is. If he suddenly had some health issue would that make it ok for you to start sleeping with other men? Not only that but buying them? No. It wouldn’t.
Don’t say anything to him. If it’s your house, wait till he goes out, pack up his shit, change the locks and text him to come and get it.
Don’t explain anything to him. And get an std test immediately. Not only has he lied to you but he’s buying other women to have sex into and putting your health at risk in the process. He doesn’t give a fuck about you so get rid of him, take your best friend on your holiday to vegas and have a great time!
Good riddance to bad rubbish. 50 and fabulous for you now.