Thanks move :) I had a long chat with him. He admitted he hadn't considered how he would've felt if I'd told him I was off to spend the day with someone I'd known for less than six weeks, and that he struggles to tell when someone is doing the whole "I need a confidence boost" thing. He's fallen for it in the past (previous relationship) with disasterous consequences, and was trying to help another 'friend' last year who invited him over to spend the weekend on her one-bedroom house boat because she needed a confidence boost. I asked him where he was going to sleep at the time and he suddenly realised what was happening.
He's lovely really, and I know he'd never do anything to deliberately hurt me - he's just so bloody naive and it winds me up when he's older and yet I have to be the mature one. He told me how scared he was about everything changing, and I pointed out that he can - and has been - running away from it, hiding and locking himself away. I told him I'm younger than him, and I can't get away from it because it's with me all the time, constantly reminding me. He's promised me that he'll think things through in the future, and that although he can't promise he understands what I'm going through, he'll be more considerate.
I'm happy with the outcome and as long as he does try, I can't ask for much more. I'm too ill to put up too much of a fight, running a fever and just feel so ill 
cheering myself up by watching the hamster going crazy and listening to the Little Shop of Horrors soundtrack.
Hope everyone's having a nice evening, glad to hear more good scan news :)