You have a problem that is not accepted except by very rare members of society. The advice that you are looking for doesn't exist. The only answer you will ever find will be inside yourself. It's a difficult situation, and I don't envy you in the least.
Let's clear a few things up first though. That you have reached your age and state that you are in love with a much, much younger man - you've known for quite some time about your sexual inclinations, and I've little doubt that you've visited gay beats / clubs / other places where you can meet such men, very likely engaging in the occasional liaison.
...you love your wife, but the truth is, it's a 'me' love (a selfish love)- ie. you don't want to lose her love. True love for her, means :
- wanting her to be free to make her own informed choice of who she loves (your current situation is forcing her choice down to a love by deception),
- respecting her and her ideals (genuine partner love really can't exist in the absence of respect)
Every time you engage in this sort of thing, you engage in the act of deceiving your wife....as you do so more and more, you have to justify to yourself why you do this. The justification you make up is just a deception...if she doesn't want you to be with anyone else, any justification you make is just a deception to yourself.
The man you are in love with, doesn't care about monogamy...because he's quite alright with you sleeping with your wife, and him at the same time. He doesn't care about loyalty because he's trying to 'steal' you. He doesn't care about respect, because he most certainly doesn't respect your wife. He might care about them if it was done against him...but this is a 'me' love. The real truth is - he only cares if it's about him (ie a 'me' love). You might be in love with him, but it's a love of this guys surface...with the rotten core hidden in plain sight (then again, we are all imperfect...but it depends on whether or not you feel safe with said imperfections)
Lastly, there's the matter of yourself. Honesty would dictate that you let the people who have a right to know (those you are in a relationship with) the right to an informed choice regarding who they are in a relationship with. It's also more honest with yourself (because you no longer have to seek justifications)...
The problem you face is the consquences of being honest...yet being dishonest also has it's consequences...
As I said...the advice you are seeking, doesn't exist. You can only find it inside yourself.