Clairey - poor you, that is a really really tough decision for you to make. I also can't believe he found the the thread - why was he even looking? Does this mean he may be reading this too?
I think only you can make the final decision about where you live, but I will give you my honest opinion and sorry if it isn't what you want to hear. I realise moving near to close friends may seem like the most comforting option for you, but is it really going to be the easiest one for you, for your dc's and for the future relationship between them and your H (assuming there is going to be one). I know it might seem like you will get the support from the friends in Kent, but it may be that they all have things going on in their own lives. Sometimes things always seem better elsewhere, only to get there and realise that actually the people back where you came from are the ones who you feel closest to - the ones who have been through childbirth with you, through the early years, through the first days at playgroup and who will be going through the first days of school with you. Other friends might be in a copletely different place from you, whereas the ones you have now will know the sort of thing you are going through (with regards to the dc's), and will be able to share the hardships and happiness of small children.
Also consider all the too-ing and fro-ing if you do want your H to see the dc's regularly. Kent to Somerset is a good three hour drive - can you imagine doing that every weekend or every other weekend or whatever? And then having the dc that far away from you if they stay with him?
I can tell you from experience that children DO adapt to new schools, friends etc, but it is quite a hard time for all involved and maybe if you and H are going to seperate leaving some of their routines in place at the start would be best for them.
This doesn't mean staying in the area would necessarily have to be for the long-term, especially as you say you don't particularly like the town. But would it be easier to stay there for a while until things are a little more settled? Can your H not move out and find somewhere else to live, and leave you in the house you are in? That would also give you a bit more time to look around for schools, preschools etc in Kent if you do decide you would rather be there.
I just wanted to give you another point of view. Have you got anyone in RL (mum, sister etc) who you could discuss this with? You are going to need their support anyway, so probably best to get them on board with whatever decision you make.
Good luck with whatever you decide. Keep talking to us. When I think back on the last couple of years and all the ups and downs of my life, it is amazing to think that the only constant (bar dh and the dd's) in my life has been you lot!! x