I'm sorry I didn't realize how upset you are. I'll try to clarify what I wrote.
A "fair weather relationship" He's steady and good to you only as long as you don't make him uncomfortable--even though he's keeping you uncertain. It appears that "fun" is what he wants, and you've sensed he might react badly if you bring up anything he doesn't want to talk about (like his ex). If you want to bend over backwards, you could send him an email saying that you've been over your ex for over 2(4-6) years and you're happy that he's found someone else he's attached to. And you gave your friend only generalizations about how much you love your sexual relations with him. -- Unless something you've already said would force you to change these words to make them ring true.
If you think he's a really shy guy and terribly afraid of losing to any possible competition, it might be worth such an email. An email will get read beginning to end without the interruption of a sudden reply, and it invites him to respond in a more thoughtful way than a text message does. Thus email correspondence provides a way to negotiate a breakup or a reconnection with greater time and flexibility than texting. Texting is more suited to flirting, surprising, throwing curve-balls, headstrong reactions, and even brush-offs, such as you got from him.
What do I think of his text-brush-off? He's a chicken, fair-weather lover. If you write the email I've now suggested, you're erasing his only justification(s), so he'll either have to get more real, or just keep on hiding. If he's hiding and you're NOT begging, you can regain your self-confidence sooner. There's a cute John Mayer "love" song for his way of acting" "I will beg my way into your garden,
and I'll break my way out when it rains,
just to get back to the place where I started
and then do it all over again."
Name of the song: "I don't trust myself (with loving you)"
Summary: Closure is something you have a right to pursue, for your own recovery of health. But don't give away your power and dignity by pursuing physically or begging to return (in effect) to his "don't ask, don't tell" relationship rules. I've known several men in your age bracket in my men's groups, and it's really quite normal for women to start wanting more explicit commitment at 3-4 months in. Otherwise most cannot feel enough trust to let their good-behavior and other guards down so verbal and emotional intimacy can deepen. In my textbook Love & Intimate Relationships: Journeys of the Heart (published in 2000) I call that the "deepening stage." I've also seen that few relationships that are mostly "fun times" will ever last, because without some serious rain, gardens just don't grow. That is: you need adversity, need fear, need anger, need hurt, shame, and defeat, and need worry and sorrow to grow a sturdy relationship that will stand the test of time.
But many women, including my in adulthood stepmother, will not seek much more than "fun times" with a man until their children leave home. That's why I have to mention that.