hi ccm, big congratulations to your ds on standing up on his own 
I know what you mean about feeling angry that you haven't got anyone to share his achievements with, all I can say is it does get easier with time. I remember looking at ds1 on his first day of school and knowing I'd made the right the choice for us both. He was such a happy little boy and I thought to myself, I did that, despite everything and that made up for ex not being part of it IYSWIM?
Your concerns about traits from your ex being passed to ds is exactly how I feel about ds1. My ex always had a naughty streak in him, I think it was down to undiagnosed dyslexia at school which meant sheer boredom, he has a very high IQ but has never been able to do it on paper. I've worried that ds1 would be the same but fingers crossed, so far he's edging towards being a nerd! The complete opposite of ex, and me too!
Its quite ironic how ex got into heroin really. We met up North, near Liverpool. We had been together for about 2 years and decided to move to Wales as it was all getting a bit hectic up there. We both smoked weed at the time and went out drinking, pretty normal activities for people our age, I was 18 at the time. But I was getting bored of it and watching our friend try more different drugs, pills, speed etc was scary. I just didn't want all that in my life. So we moved away from it all
Ex got a job which involved working shifts and all the lads on the night shift smoked weed. What I didn't know was that some of them smoked heroin as well 
(I was really affected by the Just Say No campaign with Zammo and grange hill and really did believe all the posters and hype of you will die if you take heroin. I wasn't particularly anti drugs as enjoyed a spliff but heroin has always been a dirty thing to do and a complete no no IMO.)
So ex started smoking it too. I didn't notice as he would come off a night shift and go straight to bed anway. Then be fine by the time he woke up.
Even though I was only 19 I knew I wanted a family, I thought I was with my soul mate, so packed in the weed and drinking and I got pregnant the first time we tried.
Ex managed to hide it from me really well. But there were thingsthat just never added up and looking back I ws too knackered having a new baby to really want to confront it all.
It all came to a head when ds1 was nearly 2. It was the day after boxing day and we were having a party at our house. ex disappeared for ages in the bathroom and wouldn't open the door no matter how much I knocked. When he eventually came out I went in there and was searching the room to see what he could've been doing. I noticed the bath panel wasn't quite sitting right, lifted it up and found his stash of gear. And all my missing teaspoons!
Writing this now is like writing about something I've seen in a film or read in a book. Just doesn't seem part of my life. But it tore my world apart at the time
At the end of the day addiction is addiction, whatever substance used. I think ex could've been an alcoholic quite easily. In fact, that's what he does now instead of drugs. Much more socially acceptable too. It took me a long time to realise that if you live with an addict you will always come 2nd place to their addiction. It's not that they don't love you. Its just the addicition and satisfying it always comes first.
I found it easier to accept that with regards to ex's feelings towards me but still can't get my head around it in relation to ds1, who to me is the most amazing person, I just can't imagine anything I would put before him in my life and that was one of the hardest things to accept.
It sounds like you have sacrificed a lot to be in a relationship with your ex and it must hurt that he has done this to you and your much waited for ds 
I know its a cliche, but you can't help an addict til they want to help themselves. Please don't let him put any of the blame for his behaviour onto you.
I know if I had not had ds1 when I found out about ex's using I would've stayed with him for longer and tried to fix things. But when there is a child involved, I think they have to come above everything else.
If I was in your position, I would want ex to prove to me he was sorting himself out for his own sake, not to get me back.
Got to go, really didn't mean for this to be so long. Hope you're still awake 
PS. With regards to seeing 2 parent families, remember when you wanted a baby and the world seemed full of pregant women? I remember feeling just that too, but it does pass. And it helps sometimes to have a proper look at them, do they really seem all that happy?
Take care
L8 x