How can I break up with my boyfriend nicely?

My boyfriend and I have been dating for over 2 years, but ever since we moved in together, things started going downhill. I was like, madly in love with him when we first met, but now all we ever do is fight and bicker and we're nothing but bitter towards each other. We can never seem to see an issue eye to eye. We both moved to the same city to go to post secondary, but now we're both living in our own places. He's still got a few things that belong to me like my 200$ microwave, my king size duvet and a bunch of other miscellanious things, invluding my cat but he said he'd bring her over tomorrow. For the last 3 weeks he's been constantly with his family since his mom's bf ped away of cancer (so it's not like it was a surprise) but this has put a huge strain on our relationship. I won't go into the details, but I'm not breaking up with him because Brian ped away, we've had many problems LOONG before that. I just want to know how I can end this unhealthy relationship, but still remain friends with him and get my stuff back. Any useful feedback is welcome!