'He's still being the victim and telling me it's all my dds fault.'
Of course he is, because the alternative is that he acknowledges that he's an adult who's capable of taking advantage of the power he has over a 15 YO girl, and that won't fit with the kind of person he likes to see himself as.
He may well be a totally OK bloke for the other 90% of the time (my DH was) but you shouldn't let that block out the fact that he's alright with scapegoating your DD1 and trying to get you to collude with him.
My DD didn't want her Dad to leave (although fuck knows why given how he treated her) but I totally shouldered the responsibility for the decision that he couldn't stay.
Regardless of how he might spin it to other people, regardless of whether DD would blame me or herself for what happened, regardless of the fact that we'd been happily married for 15 years, because I just knew that I was doing the right thing for the right reasons.
Yes, it'll be hard going until things settle down again, but you'd be in a far worse place if you listen to the flannel he's giving you about it being your DDs fault.
Always turn it back around onto him, never go along with him saying he's justified in treating your lovely DD like shit on his shoe, and don't let him drag your younger DD in. This is the time to your DD how she should expect to be treated by those around her 