My dear, you are a few months into a long distance relationship
Therefore if we look at the 'currency' generated in a relationship where you are not living in different parts of the country/world, the fact that you know this guy a few months at long distance means that in real terms it's all about YOUR perception of what he says/is/means. The currency going into the relationship bank balance is imaginary.
To build the balance, it's all about Actions not words.
Bear in mind that with a LDF words is all you have really, and he is already TELLING YOU that you're not on his radar as much as he is on yours. I think - and this is extremely common in OLD and LDF - that there is a massive amount of future faking going on in your relationship.
If he's telling you just enough to keep you calling him, then potentially it's cheap talk because clearly, he's in no position to make a proper go of this relationship any time soon. he can make all the future promises he likes, because it's not actually going to happen. I would also expect that even when he DOES move out, the kids won't be told because it will upset them, he'll keep you at arms length etc and you will be no further forward. At the moment I suspect you are the sticking plaster for his ego, you are softening the blow, but not someone he wants to be with long term. You may even be something he knows he has over his STBX.
If you are driving this, then you are - and I mean this gently - conning yourself into imagining a relationship that in all probability isn't there. He has done very little to earn the title of BOYFRIEND.
I have done OLD and tbh the 'Oh my kids are my life' lot are just paying lip service a lot of the time, so I do
whenever I hear it. I'm a FT parent and have always enjoyed some level of ME time, even if it's just after DC bedtime. I know you know this and feel similar, and perhaps having a bloke that is miles away means that your priorities aren't challenged, I get this. My OH, when I first met him would spend every weekend either away with his DC or have DC with him, it meant that he and I saw each other during the week and at weekends I'd have time with my own DC and life balanced well, nobody compromised.
For me, this guy isn't ready to date. He's still living in the family home and the day that he leaves or gets the divorce will be a tough process to get through and his priorities and perspective will change. YOU are not his therapist, that's not a role anyone should ever take on, it ruins the relationship dynamic.
In short I think he has not grieved his relationship, he's done that bloke thing... NEXT!
If you were my best friend or my DD, I would recommend that you tell him that as lovely as he is, that you want more than a part-time relationship with someone on the same page as you. someone who knows what they want, has had the time to process and heal from the breakdown of the relationship with the mother of his kids, who's settled into a childcare routine, etc etc etc.
I would say the same to a man if he were dating a woman still living with an ex.