Hi there Tea,

B is a bear. My advice would be to work up to it, with strengthening, and also to explore some alternative voicings of the chord which may work in some contexts. Perhaps the easiest B that works to replace a B Major in some contexts is a B7 chord. Try the non-bar-chord version.

I have couple of tutorials that might be helpful for you. The first is a set of finger warm-ups and strengenthing exercies. Here is a link to that tutorial: http://www.guitartricks.com/tutorial.php?input=424

The second is a series on Open Bar chords, which offers some alternatives to a straight-up B Bar chord, which may work in some contexts if you like the unusual harmonies brought in by the fact of the chord being "open". Check out the tutorial and you'll see what I mean. Here's a link:
http://www.guitartricks.com/tutorial.php?input=432

Good luck and have fun! - Lisa McCormick