Hi and thanks for the replies. I've been trying to spend as much time as i can with him during the day, involving him in stuff with L such as nappy changes, bathing, and encouraging him to hug his little brother. I know he is still struggling with his arrival and so we try and give J extra cuddles and kisses and tell him we love him lots. Last night he went to bed at 7.45 (we were just running late with everything) and he went straight to sleep, but we can't do that every day otherwise we'd be eating our dinner too late (there are limits!). Once L settles more i'm hoping that will help J - L has colic and so has been crying a lot and needing more attention (we're due to have a second appointment with the oesteopath for that, which has already helped a lot).
I think the main thing will be 'time' and just constant reassurance (and sleep....)
Thanks again
t x