Can Depression Itself Lead to Sexual Dysfunction?

I've tried searching for quite a bit now, and find that most people talk about sexual problems linking to depression medications. What about just plain depression without the medication? Doesn't that itself lead to a loss of sex drive also? I think that's what I'm suffering from currently. I haven't seen a doctor for it, nor have I taken any medications. Most of the time I find myself trying to fight depression, and it seems to work sometimes. I think knowing that you're depressed helps a whole lot. Ocassionally, I find myself saying to myself, why let this bother me? Or I may sometimes sayto myself, just don't think about it. However, what I can't seem to fight off is whenever something really bad happens. Then I'll lay on my bed and stare at the ceiling for about 30 minutes thinking in detail about the horrible situation. Is that considered depression? Even if I have something else to do in the meantime, I would still have to allow myself to think about the horrible situation before anything else. And once I'm done thinking about it, I still feel horrible/down. Now as for my sex drive, it's been very unusual. I tend to masturbate more often than I have sexual intercourse with my wife. But for for the past year in a half now, I've been having a very low sex drive. I can sometimes go for days of not having the thought to masturbate, and this is unusual for me especially. I find that my penis no longer gets hard as before, and I almost always ejaculate prematurely. Whenever I start to masturbate, I would lose the drive in the middle of it. My penis softens up and I no longer feel like continuing. It's like I just lost interest in the middle of sex. However, I find that if I try to ejaculate earlier, I can still do it. But of couse the feeling is still not the same like before I ever had any sex issues. I'm actually afraid to have sex with my wife now because I'm too afraid that my penis will just die down in the middle of it. I'm pretty sure it will too. I still get aroused by looking at sexy women, but when it comes to masturbating, it's almost never satisfying. Forgot to mention, I never really had this lost of sex drive until I smoked marrijuana for a little over a year. I remember everytime I smoked marrijuana during the night, I would masturbate and ejaculate. It was the best ejaculation ever under the influence of marrijuana. But unfortunately, I lost the sex drive eventually. I've come to a conclusion that marrijuana is what led to my depression, and that depression led to my sexual dysfunction. Can this be correct? Or is that marijuana is the cause of it all.