reciprocating oral

so I need some opinions/advice.... I'm 17 and I've been seeing this guy for about 3 months now and we both really like each other and are exclusive but we're not "officially" a couple yet. He's fingered me a couple times and I've blown him twice. I've never had an orgasm from him just fingering me (or ever) but one time I got really close from just kissing and literally him touching my nipples(?!?) anyway I want to known what I should do- like is there a subtle way for me to tell him I want him to go down on me without just outright saying it?