I've been T1 for over 20 years now. Other than normal impotence reasons (nerves, too much drinking, etc), the only other times I've had a problem is when my blood sugar goes low. Unfortunately, when I first hook up with a new girl the anticipation can send my blood sugar down. Which sucks! But 90% girls could really care less. If they like you, they're usually fine with waiting a few hours or until the morning.
I've even gotten laid practically because I was diabetic. Some chicks get turned on by needles and dudes with conditions. What can I say? Girls are crazy and I'm more than happy to oblige them. Seriously, take your shots and test out in the open at parties and such. You'd be amazed. Everyone else seems boring and lame when your shooting up or pricking your finger.
Without a doubt, your issues are in your head . . . the one you use to think ;)