First of all - welcome to the club - not as exclusive as it once was, but always room for more!
Diabetes can eitehr be a positive thing or a negative thing depending on how you look at it - I know many diabetics who stop everything for fear of things going wrong. I also know many diabetics who work with their diabetes to allow them to carry on doing what they do - but the outlook each group has is very different. The negative one is very negative i.e. it stops me doing anything I want and the positive group is more like - I've got this added thing I need to consider and work with, but it isn't going to stop me doing what I want to do.
I'd suggest trying to stay upbeat and positive, diabetes and controlling it is far easier than it used to be so the change in your lifestyle shouldn't be huge - there will be things you will need to change or new thigns to do, but they won't be hinderances, just other things to think about (and adjust to take into account what you are doing or planning to do).
It is a serious problem, but if you don't let it drown you then it's easily managable. Expect to be a wee bit up and down for the next few weeks as you get to grips with it all and adjust to what you are doing, but don't let it stop you doing stuff. As things stabilise you will start to feel much better, but don't expect it to be fixed in a day or so, it will take a wee bit of time, but it will get much better once it's stabilised (thing slike insulin dosages, food intake, blood tests, etc, they all go towards ensuring you are stable and things aren't going out of hand).
Biking, head out with mates and let them know what to do if you feel funny - extra rations to help you maintain control whilst exercising - don't put the fear of god into them, but let them know what to do if you do take a hypo - hypos vary from just feeling a wee bit funny to right out blackouts - but they generally don't just happen (unless your insulin is very wrong)...join a local diabetic group and try to find out what you can about making it work with you and what you are doing.
Diabetes UK is a very useful group (the governing body of Diabetes in the UK - used to be the British Diabetic Association but changed their name about 6 years ago (I think) to Diabetes UK). They have a lot of contacts for local groups and teams who can offer advice/assistance. Also start getting friendly with your local Diabetes Medical group as they will prove very useful for advice and help whilst you are adjusting.
It isn't great news to be told you are diabetic (I was only 17 months old so don't remember the chat!), but it isn't the end of the world. Accept that things are going to changeand you will soon adjust to a new 'lifstyle' that should allow you to continue doing what you do but also make sure your diabetes is very weel controlled.
Email in my profile if you want a chat if that would help - there are a few diabetics on here, and I'm sure they would all be quite happy to have a chat with you if it helped.
Sorry for the long post!