I say go for it SH. Going to dinner or a movie with a guy isn't a big deal. it's just spending time with a "friend". I wouldn't jump into bed with him right away or anything but going out on an innocent date, nothing wrong with that at all.
I think he's liked you for a long time. That would be my guess as to why he's still asking you out when you're pregnant. He really does like you.
so go out and have a good time.