(((Bella)))
First of all, nothing you do can make him use. The 3 c's...you didn't cause it, you can't cure it, and you can't change it.
Just so you know, I'm a recovering addict, but also a recovering codie (codependent) who has been in relationships with 3 A's (addicts). I know both sides of the fence.
Your gut is telling you he's using, and I would go with your gut. It won't do any good to confront him, because even if you catch him red-handed, he will probably make up something or just deny it.
Another thing is, don't just assume he WILL go back to being a clean/sober person, the one you fell in love with. There is no such guarantee with addiction.
The best thing I can recommend is finding al-anon or nar-anon meetings and reading books about codepency. Melodie Beattie's "codependent no more" is an awesome place to start.
And as far as your party stressing him out so much? I'm sorry, but this is just an excuse. I was robbed at work 2 weeks ago...had gun stuck to the base of my head, then was hit in the head with a gun, requiring staples in my head. My coworkers/friends were also hurt. I wanted to use, I won't deny it. But I wanted recovery more, so I came home and reached out to friends on SR.
If he truly wants recovery he will find it. The only thing that helped ME, was for the people who loved me to let me hit my bottom and figure out how to pick myself up. I knew they loved me, but they did NOT give me money, or a roof over my head as long as I was using.
Whether you stay with him, or not, is your choice. Just remember, you have the right to determine what you will and will not tolerate in your life.
One more piece of advice....trust his ACTIONS, not his words. If he is using, his actions will show it, and I think you've already figured this one out.
Stick around...there are some wonderful people here with ES&H (experience, strength and hope).
Hugs and prayers!
Amy