advice on how to change MY mindset

I need some advice:  clearly all of us are posting here because we are unhappy.  For myself, I have run out of things to try and I am done trying to fix my marriage.  There is no marriage.  We are roommates and nothing more.  Having said can I change MY mindset to be a more positive person overall.  It is a real struggle for me right now.  During the Lenten season I try to not only give up something (TV after 8pm) but also doing something.  I am not comfortable in my own house, I look for reasons to stay out, which is not fair to my sons (ages 15 and 17).  DH and I don't fight, we don't really talk at all and we are rarely in the same room even.  I have started ready a daily Lenten meditation/Bible verse type thing to set my priorities straight, but other advice would be great.  At my job I am an upbeat, positive person--I love my job so it's not hard!  I teach 6th and 8th grade and am the Assistant Principal of a small Catholic private school.  I adore my students and there is no way to be grumpy when you walk down the halls and hear the kindergartners singing, see the first graders painting, watch 4th graders in PE class, watch an 8th grade science lab where they are burning potato chips to measure the energy being released.  I love my job.  But I walk in my house and BOOM-it's like the door of a safe slams shut.  DH brags quite a lot and I just can't stomach it, so I usually don't talk about my work at home.  How can I stay positive in the face of the weirdness I live in at home.