Let's say you just had an incredible night with the new person you're seeing. The conversation crackled; the hours over dinner flew by. Come Monday, though, you start to feel that something isn't right. They come up with excuses that strike you as flimsy, and they start responding to your texts with a detached "haha" or "nice." You end up feeling anxious, confused, and lonely when the weekend rolls around.
If you're dating someone who backtracks after deepening intimacy with you, it's possible that they have an avoidant attachment style. Whether that makes them a viable partner is neither here nor there; if you're interested in learning how to support and love someone whose personality aligns this way, you can learn from psychological studies on the matter.