When I was in my early twenties I dated a girl for 2.5 years who came from a religious family. She was a virgin and remained a virgin for the entire duration of relationship. She wasn't particularly religious herself, but her parents were (particularly her mother who was on her way to becoming a nun before she met her husband), and her abstaining from sex was entirely out of fear of what her parents would say (this was a girl who was 20 years old when we started dating).
So I waited for her, patiently. I didn't pressure her, I didn't tell her she was going to have to have sex sooner or later, I just respected her her wishes. She never explicitly said "I'm waiting for marriage", I had to figure that out for myself. Being young, she didn't realize that you're not really in a relationship - you're not truly a couple - if you're not sleeping together because that's what couples do. She had a grade-school idea of what a relationship was, and not wanting to be lecherous I went along.
Then one day I heard from an eyewitness (a good friend who I trusted and who had no reason to lie) that she was making out with some other guy at a bar. I ended the relationship after that.
Its funny how you lose perspective when you're in that kind of situation. You don't want to be a lecherous creep, and you want to respect the person's wishes so you convince yourself that it's alright. But once you're out of the relationship, you regain the ability to view the situation objectively and you realize how stupid it was for you to stick around, and how pathetic it is for someone to put up with that. You realize that you weren't really in a relationship at all because intimacy (i.e. sex) is a core feature of a relationship - it's what you do together that you don't do with anyone else. That's what a relationship is about. If you're not having sex, then you're not a couple, you're just a pair of people pretending half-assed to be a couple. I was with her for 2.5 years, our parents met, we even talked about moving in together but even in light of all that, I don't refer to her as an "ex", because I don't see what we had as a relationship. It was just a childish charade.
I've never spoken to her since (this was over a decade ago), but I imagine she's must have started having sex with her boyfriends eventually (because how many guys would stick around for 2.5 months without sex let alone 2.5 years), and that after maturing, she now realizes how ridiculous it is to not have sex with the person you claim to be in a relationship with. I'm not bitter, but I do hope she looks back on our "relationship" with regret, and realizes that she was in the wrong. (I don't mean about making out with another guy, I mean about abstaining in a relationship and with someone who was willing to wait for her for 2.5 years). Frankly, I'm glad she was caught making out with the other guy, because it meant that I didn't have to break up with her purely on the grounds that she wouldn't have sex with me. I was a young man, and she wasted 2.5 of my best years with that pretend, kindergarten "relationship". That's 2.5 years I could have spent in a real relationship with a person who really wanted to be with me (not just pretend to be with me), and in retrospect I wish I'd payed more attention (or any at all) to my own needs rather than just ceding to her needs which were irrational and childish.
Silly religious customs and crazy parents aside, having sex is what couples do. That's why humans come together as couples. That's why cheating will end a relationship. You cannot divorce sex from relationships. Without sex, it's not a relationship, it's just two people being in close proximity together. If you want a real relationship, but the other person wants a pretend relationship, then you're obviously not meant to be together.