ampm I am so sorry to hear this - some of what you've experienced is similar to me - similar age (we're not too old to post ), same age daughters, same hostility from DD at start - and a new DP living several miles away (my troubles only started when he and I bought a house together).
What seems significant is that his behaviour changed, from what you say, quite suddenly. If he says he has no answers, he is probably being economical with the truth - he may have answers that he is afraid of voicing, because he thinks they may hurt you and make HIM feel bad about himself - not realising that having NO answers is sheer torture for you and just prolonging the agony.
Have you asked him straight out if he has met sometime else? You say you have only texted in the last month. Have you actually spoken on the phone or face to face? In my previous experience, whenever a boyfriend started the 'want space' speech, it meant he had met someone else or wanted to meet someone else. In other words, like the title of that excellent book, he was 'Just Not That Into Me' and the best thing I could do was leave him to it and move on, no matter how much I thought I loved him.
Or maybe he is scared of this new commitment to you? Do you think he feels under pressure to commit, now that DD has accepted him, even if you are not pressuring him? Have you met his daughters and are they happy with him having a new relationship? I have a friend whose Internet-met new partner has two toxic adult daughters who will never accept her. Causes no end of grief.
Also, have you tried telling him that if he can't offer you the relationship you once had, you want to end it now, no more contact, nadir. You might find he comes running when he thinks he is really losing you, and that you are not desperate to hold onto him. And if he doesn't - then it will hurt, really hurt, but at least you will know where you stand and be able to start moving on.
I have similar problems with my current DP - long story - and I am wondering if I will have to say goodbye to him, despite knowing that he has been the love of my life. But we are ONLY in our 50s and I am sure that there are other, NORMAL men out there for us.