I think the term martyr is used obviously as an exaggeration. But the modern definition in this context is something like "person who willingly suffers hardship in order to get sympathy".
Read some other threads, make some changes, and most importantly, have the guts to see them through.
He dumps his dirty laundry all over? Don't wash it. He doesn't have clean clothes for work? Too bad for him.
He lets you make plans then you end up having to apologise to your hosts because he doesn't want to go after all? Don't make plans with him. Say when invited "I'll come along but DH will have to let you know himself if he wants to go" and then if he doesn't look after himself, just go without him. No apology needed, you enjoy yourself. He realises at the last minute that he wants to go? Great, then he gets to grovel to your hosts as to why he's suddenly there expecting to eat when they thought he wasn't coming.
Under no circumstances do you apologise or explain anything for or to him. He's grown up, he can figure it out and do it himself. He'll either get it, or he won't.
Do you think he goes to work and treats his boss or colleagues the way he treats you? No, because he knows it's unacceptable and he can't get away with it. Does it bother you that he has more respect for them than he has for you? Time to put a stop to it then. Best do it now before years go by and this under the surface resentments manifests itself into actual dislike for a selfish manchild who made you responsible for him just like you are for your children.
There's loads more, just go and read all the threads written exactly by women in your situation. There are probably some good books worth reading too.
Or don't, but then don't complain when you raise a selfish DS and a put-upon DD.