This is tricky.
Why does your "boyfriend" have a key to a place if he is not on the lease?
If you are living together then you have some legal problems with just shutting him out. I mean, you have legal problems subletting your place, but there are rights he DOES have.
I also find it odd that you played fast and loose with, well, everything else, and NOW you want to do thigs legally.
Tell him to remove his things in one week, do it in writing or a text message, and then you can freely change the locks and maybe be smarter the next time.