Bro, I think you'll want to double-check what TehVanarch said...
What I think it means: Anh = I; đã yêu = loved; một người đàn ông = a man; khác rồi = an other; (i.e. "I loved another man", suggesting you are gay, and thus deterring Your Intended from any intentions of pursuing a relationship with you)
I did wonder about that--I get that there are no conjugations, but I wondered if there could still be other rules about using verbs in ways other than simple present tense. (In Italian, we would probably use a subjunctive for this one, which is usually equivalent to certain uses of "would be"--though the conditional is more common for "would" cases. The way you'd say this in Italian would be something like, "I want that she would be mine.")
about the expression: don't ever say anything like that to a girl. you are totally objectifying a human being and insulting her: she won't just say no, she might swear back at you.
about the pronouns used: tôi and bạn is too formal to ask a girl out. in a typical couple, the guy uses "anh" to refer to himself et "em" his lover; the girl uses "em" to refer to herself and "anh" her lover.
anh yêu em. (the guy says he loves her)
em yêu anh. (the girl says she loves him)
I personally don't use "tôi" and "bạn" very often. I would only use them in situations like in this forum, when I don't really know whom I am talking to, or in a YouTube video, where the addressee is a large audience.