Never Knew

For almost a year I've been having sex with an older guy from work.
He's thirty three and has taught me how to adore rough dominated sex.
Our relationship, if you can call it that at the moment, is based purely on sex.
His cock is massive and he's extremely sexual with me.
What I like about our sex, other than what I've already stated, is we always have sex outdoors.
Not once have we had sex in a building or car. Its always outside in whatever weather is happening.
We now know quite a few places locally that are perfect for stripping off naked and having amazing times.
However only two weeks ago, I discovered by pure chance, we have the same father.
I was genuinely going to tell him, but that night as he took me anally up against a dry stone wall, he told me he loved me and wanted to have a real relationship.
I've not told him yet, and have had sex several times since finding out.
The thing is, is I've realised I'm in love with him. I'm worried it'll be the end for us, but I also feel I must let him know.