OP, you said you were friends first, which is why you are inclined to trust him and think he is taking care of you - I mean, we don't choose friends we don't like.
You say you feel like he treats you well and isn't using you - well, maybe that's true. Consciously, anyway.
It's entirely possible for someone to confidently declare themselves over an ex, and believe they've over an ex, whilst still having feelings for them. When we leave a relationship, we want to think we've done the right thing so it doesn't hurt as much. Denial is quite a common state of mind in the healing process.
People do not make shit up when they're drunk. They're just more honest. Maybe he didn't want to think he wasn't over his ex yet, but now you know the truth: he isn't over her yet. Not fully.
You've been talking whilst they've been together... they were together, so those words were a fantasy. You've been actually dating a couple times a month for 4 months... so, let's face it, your 'relationship' is about a week and a half old. It's still early days.
I suggest you break things off now whilst you can preserve the friendship. He needs some time to not date anyone, and ideally, to not talk to you.
Maybe in six months' time you pick things up again and you're back to where you were. Maybe you don't. But if you do, you'll get to start with a clean slate, with him having processed the end of his last relationship properly, and able to commit to starting something new.
If you start a relationship with someone who isn't all in (including if that person is just lying to himself), you're starting with an expiry date. And I don't know about you, but when I go into a relationship, I want to believe it could work out. This, in its current form, cannot.