I am new to it all. Wanting your help or suggestions.

I am neither Christian, nor from any super religious background.
Im not going to explain the things I have been through, but sometimes life can be a struggle. We all know this.
but recently I have gained an interest in the old and new testaments.
And I want to study them, and decide if I should follow Christ for the rest of my life.

But the state of things. For me, might have to change.
I am a male 18y/o, trying to build and further my career.
But I feel this tension?? or almost good like feeling in my chest when I think about following christ. You know I want to be taken seriously. But most of all I want self control.
But today I fully realize I must sin quite a bit. I been learning bits and pieces but want both testaments in my hand to really get into it.
I smoke a lot of dope,/weed/,cannabis
I have a girlfriend of multiple years. We do sexual things.
I also have an issue with relieving myself/lusting. I have since a young age as sexual things were pushed onto me as a kid. and have come to realize that its incredibly self centred and I should stop.
I don’t really know what I am expecting from you all.
I want to hear what you have to say, or to advise me wrong from right.
I just don’t ever want to lose my girlfriend, or our love for each other. She is whom I want to marry.
and the thing that doesn’t sit right with me is that I hate that I want to relieve myself, but whatever is seen isnt seen in a loving sense but just to get off.
I try and tell myself things but I need guidance.
I wouldnt ever cheat or even flirt with another human, and I dont want to argue that if I really did love her I would have stopped long ago 😞 It really is a hard thing for me. I love her to bits. I want to stop most if not all sinful things in my life.
Please, say your word.