Christian vs. catholic in a relationship?

i already know there are christian catholics/catholic christians ... whatever you want to call it ... but my question is about catholics who believe that the way you get to heaven is by what you do, not by what you believe. so i am a christian and believe that you get to heaven if you believe that jesus died for your sins, and i am in a relationship with someone who is sort of catholic but mostly agnostic ... what can i do/say? the ONLY reason i am concerned is because i care so deeply for him and i am so afraid of him not going to heaven when he dies :-( the thought of it is so heartbreaking ... but at the same time i want to respect his beliefs, or lack there of ... and i really don't want to get on his nerves about it. he already knows what i believe and that i am concerned about him ... so i should just let it be, right? but then i feel guilty for letting it go, like it would be my fault if he went to hell :-(