agree with Chouette

It depends on the relationship you have with that person. If you're very close (and if you're brave), you can ask him/her. Otherwise, you can carefully observe him/her while with you; some people might suggest you to ask a friend of yours to find it out (directly asking that person) and tell you, but I don't like this kind of strategies at all. Anyway, the first thing you should ask YOURSELF is whether you really love him/her. And never forget love is always a hazard!

...uh...i feel..it is hard to say..

I would be interested to know If FZL could work here.