I really care about you but....

[anotherbadusername]

If every sentence starts like this, is it time to recognise it is not a healthy relationship?

With my sister every sentence starts like this and she just can't leave me alone. It feels stifling and controlling.

It is too much at the moment - I have recently split up with DH and am having counselling for numerous issues (UP thinks I may be bipolar).

Given your issues it's likely to be her clumsy way of trying to help and not indicative of an unhealthy relationship. Perhaps point out that it bothers you?
You've split with your DH and sound vulnerable. Don't fall out with your sister over a misunderstanding.
Time will tell if it is anything else.