No in the latter case you are not obliged to stop dating him. But, you are obliged ethically not to lead him on if he makes it clear that he is thinking in terms of it being a “forever thing.”

I can’t imagine a conversation going well where you, out of some misguided sense of proactive fair play, tell him straight up that he’s Mr. Right Now, not Mr. Right. Unless you’ve told him different, he cannot justifiably assume the latter.

So relax, have fun, be honest and if your intentions seem to be diverging, then I guess the “what are you looking for in this relationship” talk would need to happen.

But even more than “I love you”, the marriage thing is worrisome. It signals that you have the dress and church date set, and now you just need the other accessory.

Now, it seems to me, logically, that there are three approaches you can take, if you know for sure that you will want children in your life: 1) Start dating only semi-intentionally, as it were, early, perhaps even in your twenties. That is, know that, since you do want children, you’ll be willing to marry if you find the right person, keep an eye out for obvious red flags in the “could I have children with this person” department, but leave yourself plenty of time to possibly go through plenty of people, so that you don’t have to settle, and can hold out for the person who does knock your socks off. 2) Date not particularly intentionally at all when young, maybe actually meet someone you’d marry, but, if you don’t, get much more rushed as you run out of time when you could reasonably have kids, and therefore much more marriage focused in your dating approach. Or, 3) Be prepared to have children as a single parent if you don’t find the right person. (Simplifying some here, since I’m leaving out the possibility that people might have kids while living together and considering themselves committed partners, because I don’t think that fact figures too much into whether “Laura” should be marriage-minded in her dating.)

It seems to me that if you rule out 3) (or, at least, consider it reasonable for another person to be unwilling to do 3), it has to be OK to some degree to treat marriage as a “reasonable goal” in dating. And, though that can, if done in a sufficiently time pressured way, lead to “marriage or bust” and “settling,” it’s not clear to me that it has to, anymore than treating “I’d like to have some sort of sex life” as a reasonable goal inherently has to mean treating other people just as any old person to put into that slot and not caring about the person as a whole. Since 1) seems a more desirable approach than 2), people who are absolutely sure they want children would be wise to be open to getting married years ahead of whatever they’d consider their reasonable deadline for having children, but not to listen to Chicken Little “women, you’re dooming yourselves to childless unhappiness if you don’t marry in your early twenties” warnings. Which still might mean at some point, for some people, getting marriage-minded in dating in the way that “Laura” is.

Which, for “Laura”, is presumably not a bug, but a feature, since it allows her to weed you out as much as it allows you to weed her out.

On a personal level, I’ve taken a radically different approach from that; I realised when I was twenty-two I had absolutely no idea what I was doing with respect to dating/relationships, and decided to drop any pretense otherwise; I have entered relationships since then with no expectations whatsoever, just tried to figure things out empirically. But if you know what you’re trying to do, there’s no reason to deny it (and plenty of reason not to.) There’s no reason that wanting a marriage, family, whatnot can’t be central to what you want from your life, rather than peripheral/incidental, and no saying “if/then”, while still accepting that maybe it’s something you can’t accomplish, but having it as a goal. There’s really no reason to drift through life in this respect, letting the current take you where it may and being happy with wherever you end up.

Or, probably, several other reasons that I haven’t thought of, with reasons varying depending on the man.
Having sex with someone is often an excellent way to crystalise your emotions about them. I could certainly see it making clear “No, I don’t really like this person enough.”