It means he’s looking to see if there’s a situation where you will back down from your ethics.

You made it clear you don’t condone cheating and definitely won’t be dating him. He immediately wanted to see if you’d be his “friend” (and consequently give him the leeway friends often get). Who knows? In his mind, the next time he “flirts” with (love bombs) you, you might not be so insistent on your ethical stance and may even find him charming. And, trust me, that charm offensive is going to be redoubled if he senses you wavering.

To him, your “friendship” is merely functional. You’ll be one of his enablers that denies what’s going on to his girlfriend on his behalf, you’ll be his sounding board when he badmouths her, you’re his next potential conquest if his seduction can override your indignation, or you’ll experience some fucked-up combination of all three of these scenarios.

If you indeed become his “other one,” the same will almost certainly be done to you. If he claims to be polyamorous, he’s totally doing it wrong.

I call narcissist. Run, don’t walk, from this situation and go true no contact.