If your guy appears to be creating additional space between you and him, this can be for several reasons. While it's possible that your relationship is just going through a process of readjustment, it might also be a signal that he's losing interest in spending his free time around you. However, distance doesn't merely relate to physical proximity. Rather, it can often relate to emotional separation, and the sense that your guy is becoming increasingly unresponsive within your conversation. If this is the case, it's important to question whether there are any external factors (such as family problems) that might be contributing to his lack of attention.
Making negative remarks is one process that guys might use to create conflict within the relationship, and thus hint that they're not feeling content. This is especially true if the negative remarks seem to have occurred quite suddenly within your relationship. This might signal that your guy has made an active decision to use this strategy to push you away and avoid getting closer. Negativity could also suggest that a previous remark or disagreement between you two has affected him deeper than you otherwise suspected, so it might not always be a potential indicator of a breakup. Consider whether the negativity seems to be at all constructive or whether it's hurtful "for the sake" of it. Constructive negativity can simply indicate bad communication skills.
One of the most certain signals that your guy is having doubts about the relationship is consistent refusal to discuss future plans and activities. This might become especially evident if the events in question will be time- or money-consuming, like making vacation plans. If your guy intends for the relationship to come to an end, it's very unlikely that he'll be enthusiastic about discussing future possibilities of any type. This especially includes future possibilities for the relationship, such as moving in together.
Avoiding intimacy, especially when your guy was previously comfortable with it, is often a sign that he's looking to end the relationship. This should always be taken into context. People aren't clockwork, and everybody will occasionally feel like avoiding intimacy. However, if your guy avoids small gestures of intimacy (like not holding hands in situations where he previously did) along with larger ones, this might correlate with his increased feelings that affectionate gestures no longer feel emotionally appropriate.