I'm a straight male. The girl I hang out with is theoretically bi, but possibly trending toward exclusively lesbian. She periodically demands that I avoid hugging her and keep my emotional distance because she doesn't want to allow even a tiny hint of hope for romance. (On the bright side, she's a great person to spend time with.)
This woman and I have similar problems. We both turn down offers of romance from people who don't meet our standards.
In her case, she's obviously attractive. A lot of people (myself included) want to have sex with her. She has high standards and turns them all down, then complains about a lack of sex.
In my case, I'm an eligible bachelor. A lot of families would like to see their daughters married off and living from my money, not from theirs. (Since I live in Asia, the topic often gets raised by the parents before the girl.) Since these girls are not amazingly beautiful, I tend to slow down and notice things like, "I have nothing in common with these girls," and "I would have to work myself into an early grave trying to support another person," and "If we get divorced, for whatever reason, she would be able to take the little money that I do have."
Then there are women, some of whom are known to be promiscuous, who ask me questions such as "What's your wildest sexual fantasy?" before they ask things like, "What's your name?" That triggers my slut-avoidance standard. I'm not a virgin, but I'm not a manwhore.
I think most people would say that anyone who turns down dates (or offers of complication-free sex) has no right to complain of loneliness. I don't think those people can justify their "should," I just think people like telling other people to stop complaining.

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