Have a look at Meet up, there are a number of groups for single parents but they are based over in Brighton.
If you are looking for something to do when you haven't got you little one with you, there are a number of groups in Eastbourne, Hastings, Brighton.
I live in Eastbourne and it can be a little isolating, unless you are prepared to travel. My son is grown up now, or I would have been tempted to start up a group.
Have a look at some of the uk trips on here especially the camping ones on this site for some good weekends away when the weather gets better.