Are you subject to the two year HRR following the conclusion of your J1 visa?
You can marry, but if you're subject to the HRR you need to either get a waiver or fulfill that requirement.
If you enter on a F1 visa with the intention of marrying and adjusting your status, and the USCIS figures out your intention, you can be permanently excluded from the U.S. based on your fraudulent representation when entering on a non-immigrant visa.
Why not have your boyfriend seek a fiancée visa, assuming you aren't subject to the two year HRR.

