How do i tell horny christian that not everyone wants sex all the time?

It wouldn't surprise me if he's a Sola Scriptura Protestant. Let's see here, try this quote, and see what he says.

"[1] Now concerning the thing whereof you wrote to me: It is good for a man not to touch a woman.
[2] But for fear of fornication, let every man have his own wife, and let every woman have her own husband.

[7] For I would that all men were even as myself: but every one hath his proper gift from God; one after this manner, and another after that. [8] But I say to the unmarried, and to the widows: It is good for them if they so continue, even as I. [9] But if they do not contain themselves, let them marry. For it is better to marry than to be burnt. [10] But to them that are married, not I but the Lord commandeth, that the wife depart not from her husband."
- 1 Corinthians 7:1-2,7-10

If he's Catholic, you could also provide him this quote, from the gloss of the original Douay-Rheims, on the words "By indulgence, not commandment":

"He declareth plainely that he gaue no rule or precept absolutely therein, but that he spake al the foresaid, condescending to their infimities onely, insinuating that continencie from carnal copulation is much better, and that him self kept it continually."

Another quote from the same gloss, on "Better to marry":

"It is better for the said persons that be free, then to be ouerthrowen and fall into fornication. for ,to burne, or ,to be burnt, is not to be tempted onely (as the Protestants thinke that picke quarels easely to marry) but it signifieth to yield to concupiscience either in minde or external worke."

Why are you even engaging with these people?

I’m asexual as well and my theory is that people who obsessively deny asexuality’s existence do so out of guilt. Either they are legitimately addicted to sex or it has just been impressed on them that sexual attraction is sinful and they long to be free of their real or perceived problem. I think these people you describe fit my theory quite well.

Wtf?

Well if you actually read the old testament... All it says is that you should not be promiscuous before marriage; which is not the same as not having sex.

Rabbis were required to marry a virgin. No one else was.

Jesus was of the Jewish faith and he never said that the laws or rules changed....

Just cut this person off entirely! You don't need to associate with, or be friendly with people who annoy, or anger you, and aren't worth your time, and attention. Has this person hit on you, or tried to make sexual advances toward you?

This friend of yours is giving me bad vibes!I personally think your so-called friend probably has the hots for you, and is trying to convince you of something with which you do not agree. I'm just getting yucky vibes like this person is sexually harassing you, and anyone who would sexually harass you is unworthy of you your time, consideration, energy, friendship, or love! Don't give this person your energy.

Sounds messed up.

There’s little you can say to someone like that. They’re so entrenched in their religious viewpoint that they’ll always rationalize their way out. Just let them be happy in their ignorance and be at peace that you tried.

Sexual repression can lead to deviancy, people used to fetishize even the smallest amount of skin in view on a women due to it (and still happens in some countries) without proper education about sex and making something perfectly natural a sin it can stunt growth and understanding of health sexual relationships. In Japan Hentai (drawn porn often featuring inhuman sex and even depictions of children, which rose from a ban of uncensored pornography), in Afghanistan US backed sAfghan police would rape young boys as they were seen as nothing more than objects (only good thing the Taliban did was execute these monsters though monsters themselves). History has a diverse and ever changing outlook on sexual morality but now we have come to the consensus that consent is all that matters for people of age. When I was 15 I had no idea what I was doing but as I got older and met more women and learnt to communicate it greatly improved my sex life because it's impossible to learn otherwise (porn on the other hand can teach unhealthy ideas of sex and the data doesn't lie, plenty of all faiths viewing it).

You may be right about the catholic priests, they have similar numbers of amuse as places like education (though the church has notoriously buried many allegations), personally I doubt there is any place in the world celibacy is practiced by communities. even the ones that say they do. from my experience in Lebanon at least, could hardly dance in the nightclubs as all the people were all over each other as it was out of public view.

I do have sympathy for paedophiles that don't act on their abhorrent urges and hope they are able to get help, many are themselves victims of abuse but once they cross that line though they can be removed from society along with rapists as these are crimes that have absurdly high recidivism and are alongside murder in terms oof harm.

Abstinence is perfectly respectable to uphold and I respect peoples beliefs, but from puberty young people need to be properly educated about sex because many will experiment and you end up with misguided ideas like the one posted. In the US states with prudish sex education (mainly southern states) have the highest rates of unwanted pregnancies and STDS, sins happen but the damage of this one can be mitigated

Also s an ex catholic heathen, no I don't want sex all the time. it can be a healthy, fun and meaningful experience even without long term relationship as long as consent and boundaries are respected, can even be great with multiple people, if there is a god she sure made us versatile for that haha I prefer to base my morality on figures from Jesus to Kropotkin oppose to a book written by men over a thousand years ago and translated multiple time which just so happened to reflect the time period.. reading their idea of morality, relationships including sex, I was disappointed by the lack of women having an input in the texts, as a man I learnt a lot about healthy relationships from the women in my life.

As a Christian, and any grown person they should understand these boundaries and the awfulness of sexual abuse.