How do I find out if my boyfriend listed me on his life insurance policy as a beneficiary?

You can contact the insurer (if you know who it was) and ask; if you are the beneficiary, they should tell you (and they should be paying you as well).

If your boyfriend had an accountant or a CPA, you might try asking that person, too--while one does not need the help of a CPA or accountant to have life insurance, there's a good chance such a person would know. You might also try your boyfriend's family. Unfortunately, there is no good or easy way to determine this, other than contacting the likely information sources.