If he hasn’t told you that he isn’t ready for a relationship, you may be making an incorrect assumption that he isn’t ready for one.
Though his outward behavior has given you the impression that he isn’t ready for a relationship, you can’t determine that for certain without actually asking him.
If he truly isn’t talking to anyone else nor keeping his options open, there may be something holding him back from getting serious with someone.
It is better to actually ask him about whether he is ready for a relationship, instead of merely assuming that he isn’t.
In asking him, you could discover something about what he tells you that helps to further illuminate some areas of weakness that exist within the kind of relationship that you currently have with him, thereby giving an opportunity to start making the necessary corrections.
Doing this alone could end up getting him to turn his perspective around and actually start looking at you as a true relationship prospect.