I think it is great that you can confide in and trust your in-laws. That is such a blessing to have, especially since you need some support.
Without knowing what specific types of things you are talking about, it is hard to know if it is crossing the line at all. You certainly don't want to betray your husband's trust or comfort. I would not like it if my husband shared every little detail about our marriage with my parents. But I think it is safe to tell them facts about what is going on, as well as anything that is YOURS. Your feelings, your worries, your happinesses. Those belong to you. And little details about life in general are fine.
It might be hard to explain to them why you are "sad because-" without telling them details you maybe shouldn't. But as far as "what good it did"- it did a lot of good for you. It is good to have support. And good for them to know that you trust them. I wouldn't suggest worrying them unnecessarily but if you need to vent and they are your support, there is nothing wrong with that.
I would definitely stop and ask myself "would he want me divulging this information or is it private?" Then if you think it is private, you can still ask yourself if they need to know this just for their own peace of mind, or to help in some way. What DOES he think about you turning to them for support? Does he not want you talking to them about anything? Definitely keep in mind his pride and his recovery as well.
If you need more support than you feel you can get from them without betraying his trust, you should consider an Al-Anon program. You would be able to talk about all your feelings without judgement or worrying how he feels about it. But definitely keep the lines of communication open with them, it is great that you have them in your life in such a positive way.