Don't know if mine will help 
Left 6 or 7 years ago.
Ex started off seeing DS a few times a week for a few hours at a time. I got my mum to do handovers. This progressed to me being in the house when XP turned up and took DS and then to us meeting on mutual ground.
Ex found a new gf after 2 weeks. They dated for 6 weeks. He texted me all heartbroken when they broke up. I told him not to contact me unless it was about DS.
Contact changed to 5 hours per day both weekend days. Not overnights as DS was too little and XP was living on his friend's sofa.
XP found second new gf and discovered facebook. Conducted entire relationship on facebook (presumably for my benefit?) I am afraid I couldn't resist the temptation to stare at this car crash. New gf had a daughter who was in temporary foster care. She was calling XP "Daddy" within about a week. After 2 weeks, oh look, they are pregnant (I kid you not!) Both overjoyed going on about being a "real family now". They got the daughter back as SS apparently thought this relationship was "stable" 
I felt weird. I didn't care that he had a new gf or was having a baby, but I'd wanted a sibling for DS and now he was doing it first.
Contact kept waning. They would mysteriously all be "ill" for weeks at a time. DS kept coming back and throwing up all night. I was seriously concerned because I heard that they had drugs in the house but my health visitor thought I was overreacting and persuaded me not to do anything. In any case, contact was so sporadic, it became less of a concern.
XP and gf's child was born and they didn't see DS for weeks. OK, they just had a baby. They then saw him a couple of times and then split up. Apparently the break up was extremely troubling. XP claimed that he was too upset to see DS, and didn't see him for about six months.
I met a new partner. I kept him apart from DS for a while but after the relationship seemed stable, I introduced them. New partner was immediately so nice that DS labelled him "Like a Mummy!" He had no concept of the word "Daddy" meaning a female version of Mummy. Later he realised that other children had a Daddy, but he had a Tom (not real name.)
XP decided to get into contact and I agreed to meet him with DS at a soft play centre. He saw him that once, then nothing ever again. GF lost both children to foster care again. They would later both be adopted. XP was asked whether he could take custody of his son, and he said no.
XP appears to have had a string of relationships with either very young women or women with children, but TBH, I don't keep up with his activities any more, and I have no idea what he is doing. He hasn't seen DS for five years. I don't know if he has any more children. I wouldn't be surprised, but XMIL has not mentioned any.
I married the new partner and we moved to Germany for his job. DS is extremely happy and DH and I are hoping to have a baby together next year. We haven't told him about his half brother, because he doesn't remember him and it seems silly when they can't meet until he is older anyway. He sometimes asks about his "other Daddy" and is very interested in how you can have genetic things from your parents but inherit tendencies from your non biological parents. All three of us want to change his name to match ours. XP refuses to sign the piece of paper in an irritating display of pettiness. We are likely to take it to court. He has not paid maintenance in six years.