Words are cheap. Don't put all your faith in them unless you have reason to believe that the person is completely honest. Now, that doesn't mean you can't trust the person with anything if you don't know whether he or she is completely honest. It just means you can't trust him or her with certain things, which is different than just trust), and love is one of those things. There's a difference between trust and complete trust. There are people in my life who have my complete trust and there are others who only have partial trust from me.
Oh, and force him to tell you. Not physically of course, but ask him first, innocuously, and if he refuses to give an answer, tell him how much he hurt you emotionally and guilt-trip him into giving you an answer. If he ends up not giving any answer, then you should maybe consider that he just wanted the sex.
I think you should also reexamine your own reasons for falling in love with him, not just his reasons for falling in and out of love with you.
By the way, I go for friendship before dating. But I'm 0 for 3 so either my good looks are scaring them away or I must not know wtf I'm doing...