That last panel makes me suspect that Matsukawa was cracking a joke. That is, the "boyfriend" is actually Senpai, and she's making fun of her masculinity/tomboyishness by pretending that they're not in a relationship and saying that she (Matsukawa) has a boyfriend.
The yuri goggles are strong with this one ^_^
Lol...I make up happy endings sometimes too
Weee!
I was not prepared for this. It's ok, ab sempai, one day you'll find The One. At least that's what I tell myself... Let me just head desk this pain away.