My boyfriend and his depression.

Virginia
Over the past few years my boyfriend went from social butterfly to a man who doesn't even want to leave our house to get stuff done not unless it is work. He gained 100 pounds from unhealthy eating by his choice and chose to live his life over Xbox live. He came home from deployment in 2013 and was fit, happy and very active. He keeps saying he will go to the gym the past 4 years but has yet to go...Mind that he has had a two gym memberships this whole time. Years ago he abused steroids and ever since then his testosterone has been very out of whack. He does work making sure I and our boys have what we need. I have tried to up lift his spirits and of course by his side. I have even tried making new healthy foods and saying let's go to the gym together. I know one baby step at a time. However he still has a very high sex drive. I've been depressed before and got myself out of it. How can I help him? How can I get this good change started?