Littlestmummystop, I feel for you. You sound so low. I think the key here is the sentence: "I have almost no family ( my dad was my rock), few friends close by, rocky job situation and have never felt so low and lonely in my life."
To me, it seems as though you're at a major turning point in your life. It's something we all experience, though some of us push it away and do our best to ignore it. How you deal with moments like this often have a huge impact on your life from that point on.
You seem to have two major things going on: Grief and loneliness.
Dealing with grief can often take years before it's dealt with properly, even though the sad, tearful stage may have ended some time ago. To some extent, grief is a process that carries on indefinitely. Even now, 15 years after the death of my beloved mother, I can talk about her without sadness or bitterness at my loss, and feel only joy and happiness at the memories, but since the birth of my own children I get 'waves' of wistfulness, imagining how great she'd have been with them, etc.
If your Dad died only a few months ago, go easy on yourself. Although others will expect you to be 'getting over it' a little by now, you're still in the very early stages. Your attraction to your Ex may have a lot to do with your subconscious desperately wanting some point of human contact with someone who was in your life before your dad died. There's a weird sense of familiarity and comfort about that. There's not a lot you can do about it other than avoid making life-changing decisions right now and give yourself a bit more time before deciding how you want to spend the next chapter of your life.
You also sound lonely, which again is a common feeling after bereavement, even for those surrounded by family. There's that sense of 'no one will ever understand me the way he did'. Be careful you're not projecting that on to your X and making him out to be something he's not. If he was that understanding you wouldn't have left him in the first place. Exes are exes for a reason, and unless anything dramatic has happened to him in the period since you broke up, he's unlikely to have changed. Those same problems will more than likely resurface. Doesn't mean he's a bad guy, just means you're not compatible.
You've been on your own for a while and are probably fed up with being the strong one who handles everything. You probably want someone to look after you for a change. You deserve that, I'm sure, but it is better to be the strong, alone person than the sad, bitter person in the wrong relationship.
In your situation I'd spend a bit of time cementing the relationship with the family members I have left and building a close circle of friends (whether reigniting past friendships or creating new ones). Take up a hobby or just do something you've always wanted but never got round to (I got my motorbike licence). You will end up with your life feeling much more complete and won't be so vulnerable to looking for a relationship to make you feel better... which almost never works.
You may find that the job situation seems more stable/promising once you feel a bit more positive about life in general. But if not, think about where you want to go. It will give you a path to follow even if now isn't the right time to be going down it. Just having a goal will make you feel more positive and in control.
Ultimately, I don't know your ex. He may be 'the one' for all I know and it may be your issues making the relationship rocky. But only you can answer that and I think, deep down, you'll know if he is or whether you're just looking for him to provide something that can only come from within.
Good luck and don't be so hard on yourself. You've been a single parent, which is one of the hardest and most valuable jobs in the world. You're juggling that with a job and you're also going through a particularly hard time right now. Don't be afraid to give yourself a break and lean on others. You're not superwoman. But remember that friendships/family can give you more here, without expectation of anything back, than can a new man or an ex lover with an agenda.
Good luck.