i feel i must repent

From your post history, it sounds like you are feeling overwhelming guilt over some intrusive thoughts you've been having. Intrusive thoughts are natural, and (most likely) happen to everyone to varying degrees. Try to remember that it is the actions you take that define you, and not the thoughts you have. One can follow from the other but they don't need to.

How old are you if you don't mind my asking? I think if this is troubling you a great deal you should talk to a professional, who could equip you to lose the shame/alarm these intrusions cause you and to have some strategies to act positively regardless. This is a good idea in general, but if you are late teens to early thirties it might be especially important to see someone, particularly if this is a recent thing for you. Were you always feeling this guilt, or is it only in the past few years? Has the religious Satan/Demon aspect always been associated with these feelings for you or is that new? If these are new and you are in that age range I would especially recommend getting checked out, some lifelong mental illnesses can manifest in that time and the earlier you know the less pain it will cause you in the long run.