As far as I understand Bitcoin core BTC are the same as XT BTC until XT pushes its first block larger than 1MB. At that point XT BTC are different than core BTC. Whichever chain grows faster becomes the valid chain and valid BTC. Your SPV wallet compatibility depends on whether the SPV server you're using is using XT or core.
What the actual hell
Basically if I have right now 0.1 BTC , I won't have anything on XT later ? since you said at some point they won't be the same ... If this happens won't bitcoin just die ? I mean every signe bitcoiner will use their coins
NO, you will have 0.1 btc on bitcoinQT and 0.1 btc on bitcoinXT.