OP... my goodness, where to even start...
You appear to be a be a bright, articulate woman, so I think it would be fair to say that, deep deep down, you know that your DH's response is lacking in sincerity on every conceivable level. I don't think that you're currently emotionally strong enough to deal with the situation a way that an outsider would deem fitting. I can understand that your seemingly safe place has been upended and that you desperately want everything to be safe again... so you deny what's right in front of you... you persuade yourself that things aren't as they seem, that they aren't as bad as is portrayed, that your DH really is the faithful, loving, family man you always thought he was. No doubt the pain that will be unleashed if you face these facts head on may be too much for you to bear right now... so instead you choose the pain that comes with denial.
I can understand that, I truly believe you are being as strong as you can right now and that's all anyone can ask of you...
Having said that, when you have episodes of feeling stronger, please please just remember these things - he's painted the OW in this glorified light, making it sound as though he's the only one pursuing and she's pretty much deflecting his advances... that might be true for now (although to be honest I highly doubt it)... no happily married woman would agree to meet a married man (that she barely knows!!) numerous times alone, and would most certainly not go to the cinema together. She apparently refused his advances, which means she's in no doubt what his intentions are, yet she's still happy to carry on meeting with him alone. If this is all true then she's enjoying the flirtation. She's dragging this out because she's enjoying his attention, she wants to keep him interested... this will end very very badly. It's only a matter of time. She's just as interested.
As for your DH, if he was really sorry about this situation, if he was truly committed to making your marriage work, he would NEVER have met her again... not.ever. The excuses he's given about needing to meet with her to tell her it's over and to apologise for the attempted kiss is complete and utter bollocks. But I don't think I have to tell you that... you know. A very simple email to her, copying you in, ending everything, apologising to her, whatever he needed to say, was all that was needed.
When there are no consequences for your actions then there's no reason to stop. He knows you're not going anywhere. He knows he can continue to see this OW. He's in a cushy position and he's hugely aware of this.
He'll continue with this affair... he'll continue to stay married to you... he'll continue to be happy...
BUT WHAT ABOUT YOU!?????
We only get one chance in this life, OP, only one... be good to yourself, you deserve to be loved, cherished and respected. You deserve to be truly happy.