I know i’m allowed to have sex when i’m married, but can i do it anytime i want? What about when im in love? or how about sex with friends, is that fine?
Well, the latter is referred to as having an affair and is indeed, according to religion, sinning.
Well, which religion do you subscribe to? Check their guidelines.
If your Catholic, and you have sex and you’re not married, you’re a goner. 
The Ten Commandments specify adultery, ie one party is married.
As they say, check with your religion.
Cultures and religions all put some controls on sexuality. Not all branches of Christianity stress the same levels of controls.
I suppose it would depend on what God(s) you believe in and what they have to say on the subject.
Generally, sex exclusively for personal pleasure is considered sinful (sometimes with masturbation an allowed exception as being a means to gain release from sexual tension without “using” another person for your pleasure). Sex within a committed relationship is to be expected and is not necessarily sinful – but it’s expected that when possible, one will formalize that commitment before God and in a form authorized by the state (marriage or equivalent).
Note the difference between saying that “intent counts” as I did, and “it’s sinful, but you can use marriage as a loophole” as many people (wrongly) think Christianity says.
Welcome to the handbasket!
[sub]hey, did you really think I was gonna pass on this one? 
[/sub]
It varies with the religious axioms that you start from.
Paraphrased from beliefnet.com:
Buddhism - Premarital sex is fine as long as there is love and consent between the two parties, and no harm is caused.
Paganism - This could also vary, based upon which pagan system you’re adhering to. Typically, though, there are no rules against it, although sex, because of it’s nature, should “be approached with great respect and responsibility.”
Hinduism - one should remain celibate before marriage, not because premarital sex is sinful, but because the life stage of the married householder comes only after the lifestage of the celibate student.
Judaism - sex and things which lead to it are only to be permitted within marriage.
Islam - sexual gratification is permitted only within marriage.
Christianity - varies with denomination:
American Baptist - No clear guideline. Each disciple should read scripture and pray to come to a personal decision.
Catholic - Sex can occur only within marriage.
Eastern Orthodox - Sex can occur only within marriage.
Evangelical Lutheran - Does not require marriage, but only forbids against casual, promiscuous sex, as it "does not proceed from or contribute to respect, intimacy, and care of the other.
Mormon - Sex can occur only within marriage.
Presbyterian - "Total intimacy should happen in a relationship of total commitment, which marriage is intended to be." Marriage is not absolutely necessary for sex, but sex should only be had if the relationship is serious enough for it.
Southern Baptist Convention - Marriage only.
United Methodist Church - Marriage only.If it ain’t sending you to heaven, honey, you are doing it wrong.
content free since August 2002
one should remain celibate before marriage
[sub]ahem,[/sub]
ARRRGGGHHH!!!
Let’s review, shall we?
Celibate = unmarried
Chaste = not indulging in sex
Easy memory device: The Priest takes a vow of ceibacy, NOT chastity.
(and I don’t want to hear from any damned dictionary which endorses stupid, but popular usages).
What if we don’t agree with your dictionary’s definition of stupid? 
I believe that Catholicism has various levels of sin, and that wrongful sex is among the top tier (mortal sin, I believe). Do any other religions make this kind of distinction?
I’m Catholic. Are there any exceptions to the marriage only rule.
HH:
Wrong!
Celibate = not indulging in sex
Chaste = not committing sexual sin
A married couple who refrained from sex prior to marriage, are not adulterers, and are at this minute engaged in the act with each other are being chaste.
This is based on classic usage of the words: A “chaste wife” is a common term not restricted to the allegedly-perpetual Virgin Mary, but meaning a wife who only has sex with her husband.
Any knowledgeable Catholics prepared to walk teemingONE through the intricacies of Catholic doctrine on this issue?
Poly
I’ll see your “Wrong!” and raise you a “Maybe where you live” 
I predict the next step to be 'Neener-Neener-Neener". Don’t go there!
It depends on what you believe; if you follow all the general rules of Catholicism, but believe it’s alright to have sex before you’re married, then believe that.
To properly answer your question, though: I’m by no means an expert, but I think the Catholic Church believes it is always wrong to have sex with someone you’re not married to. However, I’ve never seen a passage from the Bible that has in any way confirmed this belief. Perhaps there is one, but I’ve never seen it.
Okay, I just had to get into the dictionary thing.
From Dictionary.com:
From M-w.com:
Thus, one sees the older usage as more common, while one has decided that that usage is archaic. See what you will in that.
Alan Dershowitz has
this to say about that:
I’m not saying it’s fair or moral or that Dershowitz is the ultimate biblical authority. I just think it’s interesting that the commandment against “adultery” may not have originally meant what most people think it means.
HH, I’ll refer you to Gaudere’s comments on “creative use of language” from about eighteen months ago.
The reason we have the two words in common use (so far as people see fit to discuss the morality of sex using them, anyway) is that “celibate” means “not having sex, period” while “chaste” means “not having sex outside of marriage.” Among the English speakers of my planet, anyway. YVMV*
- “…vocabulary…”
Gee, my vocabulary is different than yours! I am truely shocked!
And, once again, you’ve got it backwards. (IMN[sup]*[/sup]HO)
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- Never
p.s. - and what color IS the sky on your planet?