Every day, several times a day. I'm not really a romantic, either, but I LOVE him so much.
We went through a really rough patch when we had two small children in the house, we weren't getting along, and not having much sex (this was many years ago) I felt like I was always angry at him during this time. He pulled me aside once and said, "You haven't said "I love you" to me in months. What's the problem?" We sat and talked and worked some things out, and I understood why I was so damn angry, and we both agreed to work on some things. And it really got better. I don't know if we could have survived that Ice Storm, but we worked hard on it and we did.
That was years ago, and I never ever want to be in that place again. If think if we both weren't so stubborn, we may have gotten divorced during that bad time. But, we stuck it out, and HARD WORK kept us together. Now, we both say "I love you" to each other several times a day. He even says it at work, when we talk on the phone, which years ago, he was too embarrassed to do! (He doesn't have much privacy at his bench.)
We've been together more than 20 years.