Sorry you and your "DP" need to get a grip. 50:50, he ahs rights - no the children have rights to a relationship with both parents but in a time frame that suits and works for them.
He left her with a 2 yr old and a 4 month old to shack up with you -and his EX is very accepting of you in the mix.
That woman is a saint, to not be creating all kinds of merry hell. Her 2 yr old goes off for ONs with her EX and his straight on the scene new woman, who get to play happy families whilst she does the grunt work. She is a far better person than I am or ever wil be.
so he puts them to bed every night, been there for the night feeds, puking, night terrors etc - no.
Give the woman a break, she had a baby her partner fucks off at less than 4 months after the baby is born, because lets be honest he did not just up and leave, he had obviously been planning it before the baby was born and you to want to get the EX ready to do what you two want.
If he misses his kdis that much he should have thought of that before he left them before they could walk!!
Seriously, if the woman has been that accommodating you two need to back off and stop being so sodding me me m selfish about the whole situation.
the only honest thing you have said is - neither you or the DP know what that woman is going through or the hell the two of you have put her through and please don't tell me she was the one who wanted the split with a 4 month old and a 2 yr old most woman do not know their arses from their elbows at this point - or was he abusive, sperm donor or do you believe every lie he says.