It is hard to say absolutely how much sugar (or anything else for that matter) you can safely eat, because everyone is different. The important thing is for you to learn how various foods effect you. I suggest that, if you haven't already done so, you get a blood glucose monitor and start experimenting to see what you can eat and what causes you problems.
If you look around the postings on this site, or read up on diabetes, you will rapidly see that there are different schools of thought when it comes to diet. However, one thing that they all agree on is that you really should eat as little overt sugar (i.e. sweets, cakes, biscuits etc.) as possible. As for the rest of your diet, the standard advice that most NHS doctors and nurses seem to give is to follow a low fat and low sugar diet (similar to the GI diet), eating complex carbohydrate with each meal (i.e. lots of cereals, brown rice and pasta). This helps some people, but many find that a low carbohydrate diet gives them better BG control. This sort of diet typically entails lots of meat, fish and green salads, and on this sort of diet you don't need to worry too much about fat but you should avoid starch and other complex carbohydrates as well as sugar.
This is all a bit confusing, but I come back to where I started, everyone is different. You need to measure your BG levels and work out which approach works best for you.