wow. ok, first let me ask that (for the sake of those trying to read your post) you go in and add a few more periods here and there. it's not terribly difficult to read, but some of us wise old owls stumble a bit with run-on sentences
i'm glad you and your boyfriend haven't had sex. think about this for a sec... in the beginning you probably felt that he was the love of your life. but less than a year later, the two of you are drifting apart. (not to mention that he's a 'bad boy', which probably was part of what drew you to him in the first place... no, i'm not criticizing... it's totally normal! i don't know why but it seems to be natural instinct for us women to be attracted to the bad-boy-persona.) he cheated on you multiple times, he's got some sort of criminal background since he's on probation, you don't get to see him much, and now you're falling for someone new. aren't you glad you didn't give such a precious part of yourself away to someone who was just temporary in your life?
now, what to do about him. girl, i know it's hard, but you need to let him know that you don't want to be with him anymore. it won't be the end of his world. in less than a year, you know of three times he's cheated. he's probably STILL cheating, especially since you don't see him often these days. out of sight, out of mind. but you do need to be fair and let him know that you are moving on.
as for your cousin, please take things slow. you have a lifetime ahead of you. if you two are right for each other, then taking it slow will make the relationship much stronger than if you jump in too soon. plus, you're still living at home... and taking it slow will also be to your benefit when you (someday) tell your mother. the longer you two have been together the far more likely she'll take it seriously and not freak out.