Bf all of a sudden is using condoms, why does this mean?

Li
So my boyfriend and I who've been together for 2months, nearly 3. Has just decided to randomly use condoms. At the beginning of our relationship he insisted I get on birth control, which I just started. We had sex today and he pulls out a condom. When I question why he says "I have my reasons," and continues to put I on. This is suspicious to me because we never really used condoms. Occasionally we did so that there's less of a mess but majority of the time we relied on the pull out method. I believe he could've started using them because of a little scare we had, but I took plan B, and received a BFN on a pregnancy test I took at my gyno. 
Does anyone have any idea as to what this means? Also please don't mention anything about our preferred method of safe sex.