Yazmine - hey girly, well im not catholic but im religious so i'll try to answer some of these!!!
Condoms as a sin???? Well I suppose in a way, sex is supposed to be for pleasure between husband and wife, and to reproduce so using a condom would be preventing its natural cause and if your married I suppose you shouldnt worry about having a baby.. Never thought of it that way before but I can understand where they are coming from
masturbating is a sin???? I dont even have a clue there other than it is not being "clean" and holy and would be giving yourself pleasure when only the person you are married to is supposed to do that. Maybe someone else can add to that one I cant think of anything off the top of my head.
Homosexuality is a sin???? God made eve for adam and adam for eve not and eve for eve and an adam for adam... Thats my best way to describe it... Im not against homosexuality but thats my only idea...
Premarital sex is a sin???? Well now theres the big one cuz I think most of us teens in here have done this one! The bible says you are supposed to stay sexually clean until you are married and only to have sex with the person you are married to.
I hope that helped hunni I know its not much of real hard evidence or anything but hopefully it helps :d much love melissa