Bad situation, but there is good advice in this thread. He's having his cake and eating it too. Sure, he's fun & flirty with you all day, but you'd be a fool to think he doesn't go home and fucks her every night after putting his psychological/religious confliction aside. Stop yourself now from getting even more emotionally invested!

He may make it seem like you have all this power over him and he's under a spell, but it is quite the other way around. You are hooked and he knows it. Now he is just waiting for you to give in. The warning signs are there for a reason; his need for secrecy, no plans for leaving her, trying to appear conflicted over what he would lose with HER, etc.

He's putting all this effort into you for a reason. He already knows he is pushing the boundries with you and you're allowing it, when honestly, most girls after learning he is already in a 3 year relationship, wouldn't even let it get this far. Girl, run.