Often when my boyfriend and I are fooling around and I want to have sex he tells me "later/tomorrow/in the morning" so we finish in other ways. It is confusing/frustrating me. (by the way the "later" thing usually does end up happening but I don't understand why it can't be "right now")

If his was a girl saying "later", the guy would be seen as an asshole for being angry that she won't have sex with him when he wants.
This is cliche advice, but I personally think you should talk to him about it. I know you don't want to be pushy, but if it's been like this the whole time, and it's really bothering you, you should talk to him about it.
Of course if he has the option to have a blow job (lay back and enjoy) or have sex (requires more effort), and if he's tired at the times you're mucking around, it might just be easier...?