get a dna test, it's the only 100% fool proof way.
Oh... does the baby look like your bf? It's most likely his if your dates were correct.
Based on your due date (I used a conception calculator http://www.franklypregnant.com/calculator2.html), you likely conceived on Feb. 2nd.
I'm not very good at figuring all that out, but I'm so sorry that you had to go through that. That's really horrible.