I am sympathetic. When my OH and I met she was living in Geneva, had some school English which she had learned in her Italian speaking home area so we used French as our common language, although we came to realise we both speak the same version of Spanish later. Anyway, her English picked up enough for her to have been a lecturer in a UK university for five years. We moved here. Grand.
A couple of years ago I got ill and part of my treatment was a cocktail of cardiac and neurological drugs that wiped a large part of my head. My languages went walk about. My English was badly battered and I went back to my childhood language, neither of the required. I had to do lots of relearning with my memory very shaky, especially short term thus relearning things was easy in principle but then searching for words difficult because I had (re-)learned them and when I needed them I to often give up.
It taught me something about language I was not aware of. This helps with learning. Instead of fighting for words allow the other person's words to flow. Take in what you can, ask for repeats of some things, but do not waste an enormous amount of energy trying to find words and grammar whilst taking in what is being said to you at the same time. Patiently listen and be minimalist in your responses. That way your store or familiar words builds up, the phrases they are most commonly in or associated with slowly but surely do the same and then the connecting bits fall in place. You also begin to identify different uses that defy the rules you are used to, for example: In the English language one should always try never to repeat a word in a single sentence. A good example of that is 'therefore' which is an almost hard and fast never more than once word. Yet in French one might well use 'donc' several times in a single sentence.
I had to relearn such things and now realise that the core of language is comprehension of not just words but contexts, which is far more important than word perfect speech. So just allow yourself to fit gently into it, go for learning aids as people have recommended. Above all else, patience, especially with yourself. Losing it really can lead to losing it!
