Should I leave my husband ?

He has severe Erectile dysfunction and won't do anything about it. He has smoked for 25 years and I am sure this is a major factor. I can't even get him to take a walk with me or exercise at all. When this started about 18 moths ago I started working out and I lost 45 pounds thinking maybe he wasn't sexually attracted to me anymore. When we do try he climaxes with a semi erect penis and turns over and says " sorry " and falls asleep. So I consider him to be sexually selfish when we actually try intercourse it may work 20 % of the time. I don't know what to do . I think my marriage is over. We have been married for 20 years and we have 2 kids. I love him but his lack of effort is killing our marriage.