How to keep him interested?

Let me preface this with saying that this was my first casual hookup.

So I’ve known this guy for many years and we have gone through waves of talking and not not speaking over the years. Last week he responded to a post I made and we began talking, then a few days ago we slept together. The sex was really good and I ended up staying the night and we cuddled and talked. He did ask what my intentions are and I said that because I’m going on 2 month long trip in 2 months I don’t want to get into a fresh relationship right before a big trip. He responded with saying that he isn’t looking for anything serious either as he doesn’t have the time for a relationship right now, though I’m not sure if he said that because I said I wasn’t looking for anything serious or if that’s how he truly feels. After I left later that day he texted me saying “hey I had a lot of fun last night, thank you for coming over”. I responded saying I had fun too. Anyways, even though I don’t want a relationship the sex was good and I enjoyed his company so I wouldn’t mind sleeping with him again. How do I keep him interested? How do I go about getting him to invite me again? And how do I go about letting him know that I’m interested in a possible Fwb situation without coming off desperate and needy?

This being said I’m not opposed to the idea of maybe pursuing something with him after I come back from my trip so I don’t want to ruin a possible good thing.