We've been on a date now- but is he only interested in me?

You should have said hi regardless. Don't shy away if he is with someone. That is a great way for you to find out a few things. If you would have said hi then you could have seen how he would have reacted. You won't know unless you just do it. Often we let our minds take over and create scenarios that may not even be the case. Don't assume this or that. Just be yourself and don't shy away next time.