Most guys can't keep there hands off girl's breasts when they get the green light - so it might be thought of a a bit weird that he doesn't touch your breasts.
On the flip side, there are a bunch of reasons why he might not feel the urge to "grab a feel":
- He could be inexperienced
- He might be shy
- He might respect you to much to violate your private space in that way
- He could be really religious and it is against his religion
- He could be afraid of getting "too" turned on lol
- He might think you wouldn't let him/wouldn't like it
- He might not enjoy boobs as much as you though
These are just some of the reasons. But if you want your boyfriend to touch your boobs so badly, next time you're making out or cuddling, grab his hand and place it on your boob. He'll get the idea that you're ok with it, maybe that's the signal he needs...