My wife is secretly using female condoms and it is worrying me

I am 47 and have been in marriage for 24 years. God has blessed us with two kids who are doing well with their studies. Last year, my wife requested that I allow her to join a women group in the neighbourhood which I did but little did I know that this would mark the beginning of the end for our marriage. Since then, she is distant, we don’t connect as we used to and she has acquired peculiar habits such as using female condoms for no apparent reason. We don’t discuss anything as a couple anymore, our intimacy is dead and I cannot ask her about anything as she is always quick to say that I am stressing her. I don’t know what to make of this but I know her change in behaviour and attitude had been mostly as a result of joining this group. Apart from this, I don’t know what else she is doing without my knowledge and I don’t even understand why she is using condoms. Please advice...