Well, my wife is Russian and she's found a group of Russian girls living here in São Paulo, Brazil, all of them are married to or date Brazilian guys. There are about 8 girls that meet almost every week, and sometimes they invite the husbands too =P

When it started one year ago, I just stood there talking with the husbands in Portuguese and the girls would talk in Russian among them, but now, as I'm continuing my Russian course at university, I still don't speak in Russian because I don't feel safe to do it, but I can understand pretty much 70~80% of what they say. That made me really happy, to see my progress in the listening area =)
But still, I can't speak in Russian. I just keep babbling and usually just get tired of it. When talking to the girls, we all use Portuguese, and some guys use English sometimes.

And answering your question, I forget Russian ALL the time. When I went to Moscow in 2010 I could say things that I couldn't when I went back there in 2011. That's normal I guess, you just have to practice. I'm starting to forget even my beloved Italian, which is close to Portuguese. You can imagine what will happen to Russian if I quit practicing it.