Let me first tell you what you should not do: You should not do anything to encourage him or give him an excuse to break up his marriage. The Bible is clear: “If sinful men entice you, do not give in to them. … Do not set foot on their paths” (Proverbs 1:10, 15).
I know it might be difficult for someone in your position to resist your boss—but the only way to deal with this is directly and without compromise. If you don’t, he may only get more and more insistent—and it will become even harder to resist his advances. Let him know—firmly and clearly—that while you value your job, his attitude toward you must stop. Remember too that most companies have firm policies against such situations, and if he refuses to change, you should not hesitate to pursue them.
Don’t let him talk you into continuing this relationship, and don’t be tempted into thinking that somewhere down the road you might be happy together. If he’s willing to be unfaithful to his present wife, what reason would you have for thinking he’d be faithful to you?
The most important step you can take, however, is to commit this situation—and your whole life—to Jesus Christ. God loves you, and He knows what is best for you. And because of this, you can trust Him to guide you and protect you. The Bible says, “Blessed is the one who trusts in the Lord” (Psalm 40:4).