Ruby, I've been married for 33 years. When we got married, we were young and exercise was something we didn't even think about. As we got older, we both realized that something was going to have to change. He gained weight, I was weak and puny. So we both got involved in cycling AT DIFFERENT TIMES. He started, i tried to catch up, but found I just wasn't "in to it" then two of his cycling buddies left town and he became despondent and quit riding. gained more weight. His cholesterol was rising, and so was mine. I knew I HAD to do something, so I asked him to train me for the STP (Seattle to Portland Ride) he did that and hasn't gotten off the bike since. He rides circles around me, but we both ride, and sometimes we ride together!
I don't know what your boyfriend does to stay healthy, but you owe it to him to get him doing SOMETHING or the space between you is going to grow and grow and eventually you're going to be pushing him around in a wheelchair.
(that's a bit dramatic, but you get the idea)
It doesn't have to be cycling, but you really do need some common ground (and sitting around in the house is NOT what I am talking about)
good luck