For my mate, she cums between 1 and 5 minutes every time from fingering or oral sex. She's extremely sensitive to touch, ticklish everywhere, she shakes almost violently when her clitoris or nipples are stimulated, or even when she's just touched enough sensually.
I've made her cum in under a minute two different ways:
First, directly stimulating her clitoris and nipples simultaneously. The key there was direct stimulation of the clitoris. For her, I have to be really careful because if I rub her clitoris just wrongly, she'll experience significant pain. I place my fingertips directly onto her clitoris and rub in a circular motion with varying levels of pressure, paying attention to her responses so I know it's not going to hurt. Simultaneously, I lightly rub one nipple with my other hand and lick around and over the other with my tongue.
Second way isn't really in under a minute, I suppose, but it could be, and I'll explain why. Before doing this, I usually kiss her, do some breast play and put pressure on her vulva to make her wet if she isn't already. I then take my index and middle finger and enter her vagina with my palm facing up while she's laying face-up, slowly working down to my knuckles, so maybe three and a half inches into her vagina. I basically wiggle my fingers up and down (as if I were beckoning to someone) as I move back and forth by an inch or so. With my other hand, I lightly rub over her clit and hold her down because this makes her go crazy and she will almost flip out. She cums extremely quickly from this! Anyway, I think it could be under a minute if I were to use lube and just go for it, but that would kind of miss the point and be less fulfilling for both of us even though it'd make her cum faster, I'm sure.
She does cum from vaginal intercourse as well, most often if I make a point of having my dickhead rub back and forth against her G spot similar to what I do with my fingers above. She rarely cums if I fuck her hard or go balls deep, though it's happened, probably because it's a really thin line between pleasure and pain for her at that point.
Experience has taught me that every woman seems to have a different need when it comes to achieving orgasm. My ex absolutely required almost violent breast stimulation, needed to be on top and needed to be fucked deeply for it to happen, and getting her off through oral or fingering was nearly impossible. So, I'm not sure what help I can give you personally.
If you can figure out how to make yourself cum, you can teach a mate to do it for you. You said you can cum from stimulating your own tits, but not from a man stimulating them. If you teach the man how they need to be touched, that may change. My current mate and my previous mate needed very different types of nipple stimulation to cum, for example.
You might also need an emotional connection to really get into the act enough emotionally to cum, too.
Good luck.