I'm in a similar position. Mid 30s, good paying job with great career prospects, but never settled down for a variety of reasons. You mention that married people seem miserable, and I think a lot of that stems from the fact that they got married for the wrong reasons. They got married because they didn't want to go through life alone, they wanted a family and that stereotypical life. When, personally, I believe you should only get married if and only if you find the right partner to do it with. It's a tricky thing, because the clock works against us, especially for women, but forcing it can lead to those unhappy and unfulfilling marriages. It's even trickier because modern day life does not suit married life well, with a bunch of added stresses that can put strain on a marriage.
The fact you say you wouldn't be able to stay faithful, or that you're worried about getting bored of one another, tells me you've not yet met the right one for you. Because when you meet someone compatible on a such a deep level, boredom is never an issue.
You sound like you are on the verge of getting tired of that bachelor life, and may be looking for a longer term partner. That's a good thing. Just be open to it and let it happen. Whatever you do, don't just go looking for a woman because you want the long-term company of marriage, or to raise a family. You have to choose the woman, not the life. The rest will come natural. Good luck!