It is of course prudent to figure these things out prior to one's making such a commitment, that much we agree on. Our difference is the proper way in which these things are to be figured out. I am yet to come across someone who I have counselled where it has been the case that an unhappy sex life led to divorce, in most cases the issue was that there had been a severe lack of communication within marriage that led to problems. The thing to recognise is that marriage is more than simply a sexual union, moreover the biblical position is that sexual union should be reserved for marriage.
I actually can vouch that I am one of those who did divorce, because of a lack of sex in my marriage, but there were other problems too (e.g. emotional abuse, black mail, etc). My ex-wife and I in about a 2.5 year marriage had sex only 8 times in all; being in our mid-20s, that was harder than I think anyone could imagine. We did discuss sex prior to marriage; however, that did not lead to a satisfying sex life in marriage.
Personally, I believe sex ideally should be done within marriage overall; however, in the real world that is no longer ideal in my opinion due to economics and cultural factors that have lead the door to bewide open for pre-marital sex to become rampant (in the USA at least). I strongly believe that sex is more of personal choice and conscience, than what debatable arguments made here on CF. In then end, it all falls back to the golden rule that Jesus taught, and therefore would you have sex with the person that you are in love with (even outside of marriage), if they are willing to do the same to you?
If the answer is yes, then well your mind is basically made up; if not, then you know that you don't want sex outside of marriage and should wait. Its quite simple.
Biblically speaking there is no real clear cut passage about pre-marital sex, because OT has shown several occasions of sex out of monogamous marriage (e.g. concubines, slaves, etc). Fornication could mean sleeping around with multiple partners in order to please the flesh and not out of love for the person that one is having sex with; this in of itself is due to the Greek translation having a convoluted interpretation to English. However, it is noted that on several occasions the Bible does talk about sex within marriage more often than outside of it, which is why I can see why some people think its a sin or bad at least.
In the end it is up to you. I would suggest reading scripture and praying to the Lord to see what He says. I don't want to lead anyone astray, but I also don't want to lead someone into thinking that they did something wrong, only to find out there was no passage against it. Its tough to walk a line like the one with pre-marital sex, because of the conflicting evidence within scripture and translations, so we are left to only turn to G-d and the guidance He provides to our conscience.