distancing myself from friends (help)

Hi, from my last entry i had basically described what had happened with my friendgroup and i. a lot of people had suggested that i should unfriend and distance myself from them, which i somewhat agree with. the thing is, it's hard. it's hard to not try to join in their conversations (even though i feel stupid for asking 'what's happening?' or 'what's funny?') and it's hard to ignore them altogether since we take the same classes and sit near each other. it's sucky watching them have fun without me and not even trying to include me in things--a few days ago they went to an aquarium together without inviting me. i mean, it was the day i had returned from a trip i went to but they still could've asked, but maybe i'm just being a little salty about it. i'm kind of stuck in a scenario where i'm trying to distance myself from them but can't help but want to join in with them--it's not fun at all and i've been tearing myself apart to find out why they seemingly don't want me around anymore. 

i don't know how to bring this up to them without causing a huge issue, and it would be extremely helpful if anyone could give me a bit of advice on how to properly (and slowly) distance myself from my friends.