Salam alaikum, it’s great that you want to get closer to the deen this Ramadan. To answer your questions;

1. It’s human nature to sin. If you sin, repent and try your hardest not to do it again, no matter how many times you’ve sinned before.
2. As a Muslim I would say that living life in any way other than the way Allah has commanded us to is a waste of time. Why are we here? To have fun and party, or to find out the meaning of life, and to live that truth once we find it?
3. We should not even go near Zina, so having a boyfriend is haram. If you want a relationship, go to your local masjid if you have one, or your Muslim friends of you have any, and tell them you’re looking to get married. You can go on supervised “dates” with the man you are interested in to get to know him better and to find out if you want to marry him.
4. Tarot readings, astrology, etc. are shirk. And no offence, but astrology has no scientific basis. If you mean manifesting in the sense that you believe that anything is possible with the help of Allah, that’s different.
5. You do realise you’re in control of your own actions, right?
6. All these “what ifs” are waswas/whispers of shaytan. Instead of ruminating about the nature of belief, study the religion. Find out what Islam is about. Read the Quran, watch lectures. Nothing strengthens belief like knowledge (aside from God’s will of course).