Be a burden to your friends and family! Now is when you need them - and I am sure they will not view it that way. You would step up for them.
You do need to take care of yourself - as that is the only way you will be able to take care of your baby.
I know what you mean about the quiet, sometimes its tough with them and tougher without them. But that is your time to have a relaxing bath, make yourself dinner and do something you enjoy, so your batteries are a bit re-charged for when he is back with you.
Try and take the emotion out of it for now with your ex (I know, easier said than done). Let him have some space and see what happens. Sort regular access and stick to it. Try and keep the conversations to your son.
And you haven't let your boy down - the parents on here will testify to how happy and healthy and successful kids can be with only one resident parent. Its still a family, just a smaller one.
Glad you are seeing your HV.
And keep posting on here if you need to. Site is much quieter than it used to be but there are still loads of people who understand what you are going through and I am sure will have advice.