4 months is basically normal for a lot of people. It may be natural for you to be careful in becoming affectionate. In my case as an ISTP, I guess it would take much longer (I'm not too much into finding a relationship atm). It's natural for him to need space, especially ISTPs, in order to think things through. While he may seek peace with you, he might also seek peace in solitude. No reason to be concerned over this. You should be pretty happy about what you have.