Hey tutter - agree with everything everyone has said about hormones, adjusting etc.
My DS1 is 3.7 and DS2 4 months. Felt like you the night before I went in to have DS2. I said to DH that "..life as we know it will now change forever.." and was quite anxious about how new baby would affect our perfect little threesome and was also worried about baby's arrival changing DS1.
Glad to say I had NOTHING TO WORRY ABOUT!!!
I saw a wonderful, generous, caring, nurturing side of DS1 towards DS2 that I'd never had the pleasure of witnessing. DS2 is mesmorised by DS1 and his eyes follow him around the room. I feel that DS2 has somehow strengthened my relationship with DS1.
Luckily all our friends and family gave DS1 LOTS of fuss and attention when they came round to see DS2.
I make sure I spend time with DS1 on his own, as well as the pair of them together. We often have saturday mornings together on our own and go swimming, or go to the cinema and stuff like that.
Please enjoy this time, and don't worry, it's just hormones!!!