Your B1 was positive and significant meaning it was enhancing the response variable. The moderator in the second case has reversed the effect of B1 making it negative and still significant. This means that the moderator is antagonistic. Moderation is actually interpreted in terms of interaction plot. So, you have to plot to actually see what is going on. See the attached documents as guide. Hope they help
, Maurice Ekpenyong and Mewa Singh Dhanoa for the answers. But, my real issue is how to interpret the B1 coefficient. Because it is positive in the simple regression and then turns negative in te moderation. As Maurice Ekpenyong said, is a antagonistic fo sure. But in terms of reporting, Am I considering B1 as a positive or negative?