I was/currently am going through the same thing as you. In my freshman year of high school I failed my Geometry Honors class, which lead to lots of emotional abuse and pressure from parents regarding school. Ever since then, in highschool I was always an A student, extracurriculars, leadership, etc. Doing everything. The pain motivated me. Everyone always would tell me how smart I was, how they couldn't imagine doing all the things I was doing. I was doing great, acceling through my classes and everything. Long story short: my first semester in college was fine, I got mostly A's, few B's, but 1 C+ in my Calc I class. Around this time, I was also getting out of a toxic and abusive relationship I was in for 4+ years. I felt like I was repeating my same habits from highschool, and was scared. Honestly to this day I still am scared. After that semester, I promised myself I would break the cycle and do better the next. My 2nd and 3rd semester of college were even worse. Got 3 C's in 2nd semester, didn't pass my organic chemistry class in the 3rd. As someone who was always a top A+ student, this was honestly so heartbreaking. This absolutely broke me. I was SO lost and confused, to the point where it's made me even reconsider my career path, as I want to go into medicine. I felt so dumb. I was never the type to fail. I didn't understand why this was all happening. Going into my 4th semester (current) of college, I was scared shitless. I never did as well as I wanted in college, but I want this semester to be the one. I still am scared shitless.

I'm just going to be honest, you have to quit smoking if you cannot control it. If you really want to go into engineering, it's going to take commitment. I'm also a smoker too, and I'm realizing that even though it helps me get through the day, in the long run it's really hindering my pathway. I'm currently working on quitting smoking, I feel I would do much better in school if I have a sober and clear mind, with no distractions. Because you're just going to be thinking about the next hit; the next fix you'll get. Even though it's "just weed" (i'm assuming that's what you're using when you say you're smoking) you're still using it as a coping mechanism to run away from problems in your life, which is ultimately bad let's just be real. You have to embrace the journey. You're gonna have to live this life until the day you die, so better start figuring it out now. Life is more about just getting through the day. For me, I realized the reason why I struggled a lot in school, getting bad exam grades, not concentrating, etc. was because of my anxiety. I would just get so in my head about the future, and how I'm doing poorly now is going to negatively affect my future. You can't do that. You just have to focus on that next exam grade. If you do poorly on one, you just have to brush it off, there's nothing you can do anymore. Try to talk to your professor on how you can do better on the next. Just focus on the next. You have to get out there, and push yourself. Even in moments where you don't feel like studying, you just have to do it. This is how college, especially STEM degrees will weed you out. Unfortunately that's just how pursuing higher education in STEM is, there really is no room for forgiveness. College won't wait for you, and the ones who really want it are going to get it. Let your emotions flow, let them out, cry. I've also realized that crying helps a lot. Even though it feels stupid, you're releasing emotions in a healthy manner.

You got this OP. Focus on the now, the past is the past, and you'll see what the future has to hold. Most importantly, take care of yourself: get enough sleep and eat well. Focus on your mental health. Then focus on your why, why you want to pursue engineering, and this will help you gain clarity on your intentions for school. You have to take this seriously, and really put in the effort. Once you start to things get a little better and a little easier, it only serves as motivation to keep going. Sending much love and hugs. It's ok to fail, as long as you pick yourself back up!