I wish you luck in meeting him this evening, but I strongly suggest you do NOT meet with him alone, or at least not in your home. He has shown he can be violent and angry and you should not put yourself or your son at any risk whatsoever.
Please please can you arrange for a friend or family member to be with you when you meet him, or can you arrange for somebody to babysit ds while you meet him, again with a friend or family member, somewhere neutral - you may need to pull the appointment forward a little today, to meet him in, say a coffee shop where other people are around.
You have to show him that you mean business and will not allow yourself or your young child to be bullied or fucked around by this waster, a moment longer.
He has a right to see his child and access is to be striven for, but only if you can be sure that your son will be safe, well cared for and not exposed to drugs while he is in your ex's care.
Have you contacted Women's Aid at all? They are good at offering advice and support. 0808 2000 247 is the Women's Aid free phone 24 hr National Domestic Violence Helpline.
Summon all your resources when you do meet him. The relationship is finished. He has failed to contact his son for well over a month, he has been parading his exes all over FB, has provided no material support for you or his son and has proved to you now and in the past that he has little regard for you at all.
Keep the meeting short and force it to stay focused even if this is difficult - do not let it stray into blaming or shaming, do not ask him what he's been doing or why he has treated you like this. Stick to the point: access re your son, and financial support for his child and family bills etc.
Do try and call Women's Aid today on the freephone number, to see whether it might be in order, given his volatility and drug use, to arrange court-ordered access only. Thinking of you.