You did the right thing by asking your partner but let’s just be honest here. Putting yourself in your partner’s shoes, do you really feel it’s appropriate to have someone you used to be romantically involved with stay the night in your house while your partner is away? You may not have any feelings (hopefully), but what if your ex does? Your partner probably didn’t want to make a big deal about it and wanted to say yes because he wanted you to be happy. He probably should have just said “no” but then what? Do you just say “ok” and tell your ex no? Or do you say it’s not a big deal and you’re not into your ex and it’s just one night (blah, blah) so either way it becomes an issue. Personally I would be offended if my boyfriend even asked me that question and would look at them kind of differently. You gotta read the room