In any serious relationship, it’s important to give your partner a priority position. Yes, gents, your woman should come before football and beer!
But the phrase ‘on the first place’ is wrong. Even though we usually use the article ‘the’ with ‘first’, in this case, we don’t. We just say ‘first place’.
Another difference is that we don’t use the preposition ‘on’ but ‘in’. So, the correct sentence is not „I put my girlfriend on the first place in my life“ but instead – „I put my girlfriend in first place in my life.“
Very often in English, however, we simply say – „I put my girlfriend first“. It means the same – that she is placed above everything else. Read this, memorise it, get it as a tattoo!