I started off having sympathy with the OP but tbh it has diminished quite quickly. Every post is poor DP, poor me for being criticised, what about poor DPs son? Where is he in all this? Poor little boy I really really feel for him, he must feel so rejected by the central male role model in his life. If he doesn't have one now, I really hope he gets a lovely step dad who shows him what a man is suppose to do for his family. Don't kid yourself OP your DPs son will remember all this and your DP will be lucky if he gets a Christmas card when he's older.
This board tends to get really polarised and quite heated but it situations like this that give (and I use this term very loosely) step parents a bad name. Those of us slogging away trying to do the best we can are tarred with the same brush as your 'D'P.
Six years you have been together, 2 in a long distance relationship and 4 living together, surely he should have paid off his debts by now??? If you are supporting the household then there is no reason that he couldn't have paid them off, support himself and put enough aside to see his son, or does getting on with normal life take priority over him as well.
If you have any compassion in you, let this poor little boy spend one-on-one time with his dad when he gets the chance, god knows he seems to get precious little of it. You have no role to play here. I think the ex is being extremely generous letting you into her house, given how your DP has behaved.
I never thought I'd see the day when i would be on the other side of the fence 