(And now that I've typed them all out I'm not as mad, so I've taken out most of the expletives.)
Your friends are not your paid therapists and they don't owe you a goodbye when you haven't said a real word to them over IM for an hour and a half.
"*nods*" is not a word. It's not a part of a conversation. It doesn't "pass the ball" over to the other person and make them responsible for the next sentence in the IM. Nor does "*hugs*", "*purrs*", or any other action indicator. A conversation is words shared between two people and it takes two to keep it going. If you don't feel like chatting, don't chat. If you feel like having your friends with you on IM, then chat, damn it. (...The phrase I used to hear for this kind of situation is "shit or get off the pot".)
If somebody makes time to be on IM to chat with you and takes time out of their evening to do so and does so on a regular basis then you do have a "reason to sign in to IM". Trying to guilt them and all your other friends is counterproductive. They all have lives, and they all chat with you. They do it because they like you and because they think you're someone worth chatting with.