I don't know how old you are @nono1834. I assume old enough to make your own life decisions and that you are single and not encumbered presently. So I'll start there.
I've been the older married man before and can share some of my positive life experiences with you (they may apply or not to your situation).
If he is "interested" in you and is aware of your life circumstances.. He loves you, but is obligated to his wife (and family) FIRST in any relationship ya'll establish.
You will be cherished and loved, but probably not provided for.
You will be #2, not #1 in his sex life.
He will love you as long as you are in love with him and are sexually happy with the situation (his shared time, etc).
You will always be a threat to his "normal" way of life (being able to expose his affair with you)... So YOU ARE IN CONTROL OF THINGS once you begin.
YOU (maybe) will be obligated to be monogamous to HIM, but he will still have two lovers (you and his wife). This was NOT my experience(s), but I believe in POLYANDRY. Most men do not.. This puts you in a "needy" and "submissive" role in the relationship.
It really depends on what you are looking for in a sexual relationship..
Good Luck and Best wishes to you both..