This is a message that compels him to action: if he's threatened with the possibility of losing you forever, he may rethink the permanence of your breakup.
If there are more bad memories than good ones, it's worth asking the question if you should get back together with your ex in the first place.
In other words, you are letting him know that he can go do what (and who) he wants and you'll still be there. If you're available all the time, there isn't any sense of urgency to get back with you.
Giving him space conveys the exact opposite message: you're not waiting for him to change his mind and you're moving on with your life.
You think it’s just a matter of timing and you’re also likely to convince yourself that because you like him and he doesn’t want a relationship ‘right now’ that you mustn’t want one either.
In feeling rejected by his reluctance to be in a relationship, you decide to be with him on any terms rather than none.