very very complicated situation, help please?

ok i'll try to make this as simple as i can..

- my bestfriends boyfriend (and also my boyfriends best friend.. its complicated) had been talking to me really inappropriately for a few weeks, and on friday i met up with him and we went to town and ended up kissing, which he initiated.

- i felt terrible so i went and saw my boyfriend and told him the next day, and for some reason he was fine with me which.. i didn't understand, i wanted him to be mad at me because i feel like i deserve him to be angry at me because i did kiss him back a bit...

- this guy has now said to me that he's liked me for months, despite him going out with my best friend and him being my boyfriends best friend... he wont stop messaging me and calling me beautiful and everything..

i feel bad enough with what happened on friday.. my best friend is very depressive and has suicidal tendencies and i really fear telling her would push her over the edge.. her boyfriend (the guy) is going to break up with her because they've been having a very unhealthy relationship due to them both being very depressive and... i just.. i feel so confused and upset and low.. some advice would help.. i know ive brought some of this upon myself and if i could go back i would but.. yeah