Subjunctive Mood Clarification on "Incorrect" Usage
The "Subjunctive Mood" is a grammatical mood involving expressing various states of unreality such as wish, emotion, possibility, judgment, opinion, necessity, or action that has not yet occurred.
Example using the future subjunctive: If I were rich, I would donate money to charity.
Sometimes grammar rules are very obvious to native speakers (if the wrong word choice is used, then the whole sentence sounds funny or strange), but sometimes incorrect grammar can sound OK to us. In fact, as you may know, it's common even for native speakers to make grammatical errors, especially when the rule is very particular, like in this case. It's actually pretty common to say, "If I was ___" like "if I was rich" or "if I was your boyfriend." However, from what I've researched it is formally incorrect. So, the correct formal sentence would be "If I were your boyfriend." However, native speakers don't always use correct formal grammar and the "incorrect" form may also be commonly used, as is the case here.