When men ejaculate, they usually don't "drip". They erupt. The last few remaining drops drip, yes. But the main part of the ejaculation comes in spurts.
Unfortunately, if the experience went as you described it, then your boyfriend probably came inside you. There is the remote possibility that he half-came as he was pulling out, hence the few drops on the bed, but that's probably not likely.
You should ask him exactly what happened. About a couple minutes or so before they come, men can feel it; ask him if he felt it.
In the meanwhile, you should probably take a pregnancy test.
Good luck.