How is spousal support affected by a subsequent re-marriage being annulled?

No.  The fact that you did get married is what matters, whatever happens to the newest marriage after the ceremony isn't your ex-spouse's problem.

You haven't mentioned why it is that you are getting the annulment.  Most annulments are for reasons that make the marriage voidable, meaning that the marriage ceremony itself was lawful, but for one reason or another, the actual marriage relationship hasn't happened, for example, if one spouse refused to live with the other spouse.  However, if your annulment is claiming that the ceremony itself was void, that your new spouse couldn't legally marry anyone (for example, still married elsewhere), you might want to talk to a lawyer about whether this could get you around the end of your support.