I'm pretty much having the same issue with the woman i'm seeing right now. However, I believe she may have some expectations about when or how a man should cum. For example, I get the distinct impression that she wants me to cum almost 'on command' or when /she/ wants; of course that's not going to happen. I also get the distinct impression that she wants me to cum only with regular intercourse; something that i've done with a past partner, but have not been able to do since.
I do pleasure myself regularly, but i don't use the same stimulant. Sometimes it's porn, other times it's my imagination. I've seen people advocate periods of no stimulation to regain the sensation, but I take issue with that. Why would I deny myself pleasure when she's not around? I figure I ought to be able to have the same fun if she's there or not. Well, more fun if she's there.
I like sex and have a relatively active libido. I don't want to stifle that. :/ Would the same recommendations apply?